I'm sorry if I can't follow you here.
They way I see it, the hybrid mana makes Tasigur way more flexible. Tasigur is almost exclusively run as a commander and 3 is more freedom than 2 colours. And you don't even have to include all 3, that's just the limit.
The only way I see this rule useful in any way is for spells that aren't commanders, such as Beseech the Queen. It would allow a little more freedom there but is that really necessary?
EDH is an open format, incredibly diverse and building and fine tuning a deck is one of the greatest things about EDH. I don't feel hybrid mana gives me a lot of restriction when doing so. I very much enjoy it from a flavour perspective as well.
I know you said flavour isn't given anyway (Elesh Norn + Elspeth) but if we just go back to Beseech the Queen, this is an effect very atypical for white. White has some tutors (Enlighted Tutor, Academy Rector) but they generally are restricted to auras and similar. It is black only that has those tutor for everything most of the time (Demonic Tutor, Vampiric Tutor, Grim Tutor, Dark Seal, Diabolic Tutor, the list goes on).
Let's take a look at another example, [[Azor's Elecutors]]. This card is in my Gwafa Hazid EDH list as a potential win-con. It's great from a flavour perspective. It screams Azorius. Neither white or blue have something similar or cards supporting it (if you want to count Luminarch Ascension, white has one) but Azorius absolutely does. The whole Azorius colour combination is meant to be controlling and prevention of damage to you through the means of detaining things, tapping things, Propaganda effects and general aura "semi-removal" (think Pacifism, malfunction etc...). You can make the argument that both white and blue desperately have two propaganda effects (blue has as much as 3!) but I've never seen someone with a Mono-White deck build around Ghostly Prison and Sphere of Safety. They are included, sure, but they aren't a main focus unlike in a Azorius strategy where you get 5 of them with the according pay off card.
TLDR: Story Flavour is something that is hard to enforce as it is absolutely the player's choice what he/she includes but the colours are all somewhat consistent in what they do. Even Elesh Norn (despite being a Preator and thus evil) is actually a very white card, giving an anthem effect.
I am no expert but in my opinion the hybrid mana is at a pretty good place right now. I don't feel like I miss anything because of it.