I think sometimes a perceived flaw can make you feel more negatively about a thing than you otherwise would. Like people drawing connections between this arc and a previous one making you think less of it because you think it's a copy and paste sort of thing. But it really isn't at all.

It is cherry picking, man. Look at each element that is the same and you can easily see the ways they're different as well.

Princess? Yes, there's a princess that Luffy wants to help. But not surprising considering almost every inhabited island in the world of One Piece is governed by a kingdom of some sort. And they both play totally different roles and have different personalities. Rebecca isn't even the daughter of the king and wasn't raised in royalty. She's only technically a princess.

A Warlord. Yes, the main antagonist of both arcs is one of the Shichibukai. But the circumstances and motivations are much different. Alabasta was centered around stopping the coup d'état and civil war that Crocodile started. In Dressrosa Doflamingo has already been king for 10 years and there is no huge impending civil war driving the plot from the very beginning.

Illegal substance. They really aren't even comparable except that you can categorize them as illegal substance. Dance Powder had a fairly large role in the plot at Alabasta. SAD hasn't even been mentioned since Punk Hazard and isn't directly related to the drama in Dressrosa at all.

Criminal organization. Yeah, of course there's a criminal organization. That's just like saying both Crocodile and Doflamingo have crews. Their crews aren't even alike. Doffy has a traditional pirate crew and Crocodile's is more like a crime syndicate.

Then there are a lot of factors that they just don't have in common at all.

Alabasta: Being chased by marines, trekking all across the country, racing against the clock.

Dressrosa: Oppressed enslaved people(dwarves, toys), a big DBZ style fighting tournament, gaining powerful allies, Revolutionary Army involvement, inciting the wrath of one of the four emperors, half the crew is away in a naval confrontation with the crew of another emperor, ferrying Samurai around to look for their lost comrades, Luffy and his crew being split up several different ways all working toward accomplishing different goals...

They're really very different. And I think just naming superficial aspects that they have in common is misleading.