Of course it's a platformer. Just because HP notations pop up during combat doesn't turn it into a Diabloesque isometric RPG. It's boilerplate combat and precision jumping. Here's a video from a playlist of Skylanders Imaginators:
Are you going to try and tell me, with a straight face, that the game has more to do with Diablo than with Super Mario 3D world or Yooka-Laylee? If so, you've lost the plot completely.
Ah, the favoured recourse of fans of rubbish games: review scores. Disregarding that the games average in the high seventies or low eighties generally, review scores don't mean a thing.
Skyward Sword has a 93 composite score and it's a bloated mess with a terrible story and awful controls. Any game is going to have its detractors and its supporters, so you ultimately have to look at sales; Skylanders
rarely materially sells above a million units per title. On the Wii, the console with the largest install base in the last two completed generations and the one from the brand most associated with children, it didn't even crack a 3% attachment. Does it make loads of money? Sure, that'll happen with when a game 'series' entire purpose is to hawk cute, colourful toys at US$8 - 20 to kids, and parents that are suckers.
Perhaps you ought to be working for Activision then, because they have a decidedly different tune on the matter:
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I grant you there was a degree of hyperbole on my part in how I phrased it, but the point is that there ought to be compatibility for at least one game before a current figure series via patches, especially when it's on the same platform, and even more especially when the games are, as you say, 20 - 30 hours of gameplay and there's a bleeding year in between releases.

Ah, the other refuge: primitivism. The series may harken back in the sense that the game is used as an advertisement platform to sell toys and other merchandise to children, which absolutely did happen in the 'old days' of gaming, but any nostalgia you feel is a function of you, not the game.