The problem is, the lighter, childish approach destroyed the characters. Sonic is just a giant, pompous jerk, Tails is sitting on the sidelines, Knuckles is a completely oblivious idiot, Shadow is an edgelord who thinks friends are cringe, Amy is a giant simp who has no sense of self sufficiency whatsoever, Eggman is portrayed as a stupid, unimposing, clumsy villain-kind of ironic considering that his intelligence is obviously implied, etc.
Sonic Heroes is a lighthearted story done right-it's cheerful and somewhat childish, but not at the expense of character development (other than Tails). Heck, Colors DS did a better job then the mainline console version at doing the characters well.
Meanwhile, Sonic Lost World...hoo boy. The writing is a dumpster fire in that one-and mainly because it has an identity crisis with being serious or being fun. Like, Tails gets captured and roboticized but this has no effect on him whatsoever-no new complications with being turned into a cyborg. Like, after the Eggman boss fight, not only does he have the cyborg stuff just gone from him, he also acts like a jerk, saying he knew that Eggman would betray them and crap. Meanwhile, Eggman makes all these big threats about killing the Deadly Six's families in front of them, the big, purple lanky one threatens to skin Sonic alive, for crying out loud, but they then just act like a bunch of utter idiots. And Eggman supposedly dies, but that scene has such an identity crisis with itself it's turned into a meme. Oh, and remember when Eggman talked about killing everyone's families in front of them? In that exact same cutscene, seconds later, Sonic just makes a crummy pun in front of everyone about being cool cause this is an Ice zone. So, no, Lost World does not work with the cheerful style, since, well, it has an identity crisis with itself. None of the 2010's games work with the cheerful style-instead, they just insult your intelligence with dad jokes that would put boomers to shame, crap writing, character slandering, etc.