People have preferences for what they want/don't want in a shoe: more/less padding, thinner/thicker soles, more/less paneling, etc. Holding that constant and objectively looking at Emerica's shoes, they're still solid. They are one of the few brands that offers a slip in a cup and a vulc. That's pretty cool!
I (mostly) don't skate vulcs anymore so I can't completely comment on their quality outside of the regular G6 Wino slip on I had once.
If we look at most common slip ons out it's Vans followed by Emerica and then everyone else. People love the Wino G6 slip on and it must be good/built well if nearly half of the slip ons I see in the wild (and online) are Emerica.
Most brands seem to be making "vulc cups" with how thin and unsupportive they are. The G6 sole is a sturdy cupsole that still offers legitimate board feel white also protecting the feet. That doesn't feel dated to me, that feels like what the 1010, 913, and the new 808 from NB are doing. A haply middleground.
The squishy-ness in the G6 sole is exactly what makes it excel in board feel for a cup. It's responsive and not too hard like Dunks or some DC cups have been. That sole does not feel/operate clunky in a general sense. Maybe to you and that's your opinion because it doesn't meet your needs for a cup. However, across the board it's a solid sole that worked for Reynolds and works now for people. Why else are they making other shoes using that sole if it's not selling well enough to make other uppers on it?
I also want to add that the Tyshawn and 1010 both have considerably more bulk throughout their uppers than the KSL. Visually and material-wise. The 1010 has puffy collars
The 1010 and KSL G6 have pretty similarly padded tongues, though. The Tyshawn is thinner in the forefoot than the other two, but everywhere else is just as padded. The KSL and Gamma G6 both have thinner uppers than 1010, Tyshawn, Manteca, and Dunks so I'm confused on how you think the Emericas are bulkier. I also checked WearTested photos where they split the shoe in half. 1010 has less material in the toe vamp then the other two and maybe less forefoot material than the KSL G6 but it looked pretty close between those two.
I actually find the 1010 toe area to be lacking in board feel for what's attempting. The toe "kicks up" unlike the other teo where it's flat. It feels like my toes are not close enough to ground/board, whereas in the Tyshawn and KSL G6 it's closer and I can "feel" that my toes are responsive to make the needed movements to set up for a trick. Idk if that makes sense, but it's nuance.
I also skated my KSL G6 last night and had a good session in em for what it's worth. Felt responsive, not overly bulky while pushing around, and didn't feel dated or clunky. Flick is superb in them.
To add, my usual shoes to skate: Marana, Joslin, Half Cab (skate), Silo Sc, Quattro, Dunks, Accel Slim Plus, Gamma G6, and Blazer Mids. I'm more of a cup fanatic so I'm aware there's bias there.