Just replaying Metro Exodus and it's just so clear how much of the game's soul is missing compared to previous games because it sought out "broad appeal" and made creative decisions based on that rather than trying to just make a good Metro game.
It begs the question - we've seen so many games sacrificed at the altar of "broad appeal" but has a game ever been made better by stepping out of their niche to try get a better audience?
I think there's a fair balancing act between iterating for improvement, and then changing things to be "broadly appealing".
Dark Souls iterated features that improved on Demon Souls, without necessarily being the catch-all "broadly appealing" spin-off.
However, the Dark Souls sequels tried to be "broadly appealing" rather than improving on the core mechanics but maintaining the core elements that made the property popular in the first place.
Another good example is GTA: Vice City and San Andreas. They become more broadly appealing not necessarily because Rockstar was trying to hit every consumer demographic out there, but because they simply iterated on and improved every single mechanic from GTA 3, from graphics to audio, to weapon handling, to vehicle physics. So, by proxy Vice City and San Andreas became more broadly appealing because they were mechanically improved upon in areas that made the game(s) more fun and engaging, rather than making them more "broadly appealing".
GTA 5 is a good example of the series dumbing down its mechanics to be more broadly appealing, getting rid of the more realistic vehicle handling and soft-body deformation from GTA 4 to make the vehicle handling more accessible to a broader audience. In turn, it made people like me lose all interest in GTA 5, because I actually liked the skill-based driving mechanics and soft-body deformation in GTA 4. But it worked wonders on the sales front, so Rockstar/Take-Two don't care if they lose a few people to gain a few thousand more.