Gave this notion a bit of thought, and came to the conclusion that, despite its reputation as a lighthearted JRPG series, Tales is actually best when it's being serious and/or edgy.
The skits are fun and all, but a lot of times the humor falls flat, and they have a tendency to flanderize the cast. Comedy in Tales tends to be very 'anime', and frankly speaking it misses more than it hits. You get some memorable lines, sure, but is it really worth the cringe-inducing moments and painful mascot characters? It's amazing that Magilou didn't turn out to be an awful character. She's amazing, but based on the series' track record, she shouldn't have been.
But the serious parts of the story? That's where the games shine. Symphonia's best parts are the revelations of how shitty the world is; for example, the truth of the Exspheres and Derris-Kharlan. Abyss' best parts are widely considered to be Luke's characterization and Akzeriuth. Vesperia's best parts are easily when Yuri does Yuri things. Berseria's core is Velvet's dark journey, and the storyline is all the better for it.
Now look at the games that aren't very well-regarded. Graces, Xillia, Zestiria. Those games make much less of an attempt at tackling darker subject matter, and as a result, they feel kinda milquetoast. That's not to say they're completely devoid of serious elements, but yeah. Their tone feels very different from the fan favorite games in the series. It's not impossible to construct a great JRPG story with a more lighthearted leaning, but I don't think Tales is actually very good at it.
I half agree, though I'll go to bat for Graces most days. I think it's just balance: the story needs to have stakes but the actual journey needs to feel a bit lighthearted.