If you believe that Grimmel posing less of a physical threat than Drago makes the film worse overall, then I would ask you how they could have raised the stakes?
Easy, have them do what Dean actually talked about with the release of the second film. He said now the entire northern hemisphere is open to them because they have dragons.
Have them travel and explore other cultures. Show us how dragons will affect the development of berk, show us how someone other than vikings will react to dragons.
Make the world itself bigger instead of limiting it to a single island.
Whilst Hiccup and Toothless came together in the final minutes of Grimmel's defeat, it was the fact that they seperated that brought them victory. Hiccup was in bits when Toothless was first kidnapped. However, the fact that they had been apart during the film, and a helping hand from Astrid, drove him to act despite feeling out of his depth.
How did seperating bring them victory though? Again they didn't defeat grimmel seperately. My question is, in what way did the seperation facilitate grimmel's defeat?
This is why I do not see the ending speech as a retcon, and more of an evolution. If Hiccup had not matured past that point, the dragons would have been taken and
How is that speech an evolution? It's litterally the direct opposite of what happens in the hidden world.
We'll endure-Nevermind we give up, we'll change the world-nevermind the world is not ready, armada's can't stop us-nevermind yes it can, we have our dragons-also nevermind they can't help.
It's pretty much directly the opposite speech.
The dragons were never at any different threat than they have ever been. The only reason they were "at threat" is because the script said that they were but it was never demonstrated.
How is it maturation to get rid of the one thing you've been working towards that has made you stronger and help you endure every part of the way? That's like saying "Yeah we got anti biotics now, but we gotta throw them away to become stronger without them."
Be more specific, you're using wishy washy explenations.
Hiccup would have remained in his "Oh no, what are we gonna do without them?" phase.
I mean, yeah.
We already had that phase. It was 80% of the first movie. The goal of the characters was to get out of the "What are we gonna do without them" by actually getting dragons in the first place.
Similarly, Toothless evolved when he was away from Hiccup. During the final chasedown, Hiccup had to utilise the new abilities he'd learned with the Light Fury in order to escape Grimmel's dragons. During their time apart, Hiccup gained courage, and Toothless unlocked his true potential as a Night Fury. That's why I say they had to seperate in order to ultimately defeat Grimmel.
That seems again rather forced and because the script said so.
Hiccup and toothless were born learning new things without being seperated. This happened in spite of their seperation not because of it. In the second movie toothless found out about the back spines and hiccup started developing wingsuits without needing to lose each other.
They developed abilities independantly of being seperated, not because of it.
Remember, their original plan was not to seperate at the first sign of danger, neither was this the first time in the last 12 months since Stoic dieing that people had been after their dragons. Grimmel was simply the first viable threat. Where all else had failed, Grimmel demonstrated very fluently that he could catch Toothless whenever he wanted, and all the characters knew of his intent to allow his employers to overthrow Burk in the process.
But drago had caught toothless as well though. You forget that. Drago not only had captured toothless but brainwashed him too. Grimmel was by far not the first viable threat unless you ignore drago's existence.
The funny thing is, it doesen't even matter, because they DEFEATED and his army grimmel anyway.
It's this that makes me disagree that Grimmel made them "give up" on their relationship. As I said in the OP, Toothless and Hiccups relationship was already strained by the events in the Hidden World prior to the end game. Rather than the separation being because they gave up on one another, it was because they valued their relationship above all else that they seperated. They valued that relationship more than the confidence that being together brought them, and the power that came with working together. They didn't seperate because they were defeated, they seperated because they were triumphant in their evolution as characters.
That's the thing though.
Things have put a far bigger strain on their relationship before. Toothless killed hiccup's father. The seperation doesen't indicate value at all. Where does the value come from? You need to actually explain that.
You keep saying that it's an evolution of the characters but that doesen't make sense in regards to pretty much everything we've seen so far. How is it an evolution to go against their convictions? They saved each other countless times and are only alive BECAUSE they have one another, if they didn't they'd be dead.
You need to be more specific. You say "It's evolution", but how is it evolution instead of devolution? Stop using wishy washy vague explenations.
They had matured beyond the speech at the end of the second film, realising that, rather than Burk being great because of its dragons, and the dragons being great because of Burk, they were great individually and had grown to become powerful enough in their own right to survive.
Uh... what? How does that make sense?
The whole point of the first and second movie was that working toogether is what made them great in the first place. They started out without dragons and by working with them became great enough to survive.
They wouldn't have survived grimmel or draco without dragons.
That's like saying "Antibiotics make us great! But we need to stop using and become powerful enough to survive individualy on our own right without them!"
You don't just throw away proggress for shits and giggles. "Becoming powerful enough on their own right" yes, they did that with the dragons. The dragons were family, the dragons were part of their own right.
The previous films didn't need to be vague or wishy washy, they had an actualy tight plot that made sense when you examined it instead of using vague concepts like you are here.
The true tragedy of this is, I totally understand why you feel there was no build up. I don't agree, but I believe the reason why is entirely because of the distraction of having a bad guy. If Grimmel weren't around, and the villain were more faceless, akin to a force of nature as in the first film, they would have had plenty of time to explain this further and do a better job of focusing on the evolution of the characters, this justifying the ending more.
But the thing is, the seperation can't work in one movie, simply because it's not from this story.
Like I've said, the seperation is from the books, that have a completely different plot than the movies too. The seperation made sense in the original because the vikings already had dragons and the message was about animal abuse.
You can't mark "seperation" as character growth when litterally every single movie, special and serial has been about unity making you stronger than being seperate with no buildup. It would be forced even without a villain.
The high point of the second movie was litterally how the unity between hiccup and toothless was so strong it overcame brainwashing. The natural evolution from that is not "seperation".