That is the common opinion, though it was mostly hurt by people getting really mad about Phoenix no longer being the MC which made him come back in 5 and kind of really screwed Apollo's growth.
Which is my unpopular opinion on the series, Phoenix stepping aside as the Main character in the second trilogy was the best idea the 4th game had. By the end of game 3 he had accomplished everything he needed to do as a character. He saved Edgeworth from going down the path of evil, had his Rematch against Edgeworth who was no longer cheating (twice technically) , and then faced off against Godot and proved that he was the rightful heir to Mia's legacy.
There was nothing further for him to accomplish as a Main character and Apollo should have gotten a lot more of a spotlight (Athena being introduced in the 5th game didn't help this.)
Jap writers seem to have the opposite of whatever the Western ones have when it comes to successor stories and characters.
While our guys have no problem establishing their new characters as superior in every way to the previous ones, (sometimes even destroying the legacy characters just to bring theirs up) Asians seem get the cold feet when introducing new characters
Adding to the Ace Attorney example above, is Yakuza. We've had around 6+ games with Kiryu as the protagonist, we've seen the beginning and the end of his story, so when Like a Dragon came along, it was in the eyes of the new protagonist Ichiban.
The character of Ichiban was very well received by fans, who were ready to move into a new chapter in the franchise... And the sequel to LaD was announced.
Kiryu is back. Not only that, he gets a short DLC game about how the end of his story was actually not the end and how he has to return to wreck shit up again. To be fair, from what we saw LaD2 is gonna have 2 protagonists in Ichiban and Kiryu, but the fact that already they're cutting down on the new guy to bring back the old guy is not looking good.
Another example would be Dragon Ball Z. Toriyama was ready to put Goku to rest at the end of the Cell Saga, prepping up Goku's son Gohan to pick up the torch and lead the franchise afterwards, but nope. Goku was brought back, Gohan got permanently vanished to the sidelines.
Seriously, contrast that to say, Last of Us 2, where the legacy character gets unceremoniously and graphically killed off by the newer one, while all throughout the game the new writers retcon shit into how awful the old dude was