Persona fanbase can be a vicious and defensive one. They like their Persona games a certain style, but will support the IP regardless of what direction it takes. Devs know this and try to stay faithful to what makes the series great, building on each new entry, which in turn keeps fans coming back for more. Square and Atlus aren't in the same position when it comes to what fans want and expect. Square has the luxury to take the hate it gets and brush it off while moving into the next thing. Atlus tries to stay faithful to fans since alot of what they put out in the past was niche and catered to a small group. They didn't have the luxury to brush off outcry thinking they'd get continuous support.
I hope that makes sense. This is just my perspective though.
Except the in this case the Dragon Quest mainline series is somewhat in the same position as the Persona series in which it's heavily fan centric, especially so in Japan compared to the more Western focused sales of the FF series.
The mainline Dragon Quest games with the exception of 10 which even still is relatively faithful has been a constant in it's mechanics of having turned based combat systems over the past 30 years since the series inception, which apparently this trend even continues even in Dragon Quest XI as well from statements Yuji Horii has implied.
So I doubt how long a series has been around having dozen plus releases has nothing to do with the situation of simply changing things around to adhere to a concept of change much like how the Final Fantasy series has taken as such.
People argue for for sake of innovation and bringing fresh ideas to the table, but innovation has never under any circumstance been an acceptable substitute at the cost at the core mechanics of it's gameplay.
Pushing for new ideas is all well and good, but it serves no purpose if the emphasis on the "game" part of an actual game becomes lacking. In the case of FFXV and Type 0, they weren't entirely shining examples in this regard, when even in the face of other Action RPGs weren't actually high notes in terms of their combat systems.
Innovation is nice, but I'm much prefered for taking a proven formula that is known to work and tweak it to iron out the flaws and include things that would emphasis on the well working core that already exists even further. Persona 5 and Dragon Quest seem to do precisely this. Square at one time did the same thing for the ATB system from its beginnings with FFIV and the eventual culmination of something like FFX-2 or Lightning Returns.
There are some ARPGs that do this as well, notably the Tales series for example which have seen many iterations of it's Linear Motion Battle system which was established in Phantasia into the form it now exists in today. I'd say there are far better cases of sticking to a formula that actually works rather than just changing the whole system entirely to chase a new audience that FFXIII and FFXV tries to do.