Combos are a general feel problem? IMO, one of the biggest differences between 13 and 98 that's usually undersold a ton is the movement. Sure, the basic system is pretty much the same with buttons and hops and whatnot, but 13 has way, way more horizontal movement to it, which means poke lengths matter a lot less. 98 has a lot of that SF-style thing where people try to space pixel-perfect pokes against each other, while 13 is more about making the calls, AAing with correct angles and just going ham
combos can be part of a general feel problem because they tend to dictate what the source of damage is. it's related to the normals thing to a degree, where reduced damage on 'em can make them feel weaker than what i like. that's the approach that modern games have taken to a degree, focusing less on pokes and more on being able to take those 'risks' to the point of where they aren't significant risks anymore so you can land 'real' damage
kof13 has the combination of having normals that actually do have significantly smaller and slower hitboxes than their 98 friends, changing up the entirety of how the game is played. while the movement physics difference is true, i don't know if i can say that's what causes kof13 to have 'much more horizontal movement'. to me it's more related to the weakness of normals as a whole in comparison 98's monster-ass normals- effectively, you have more reasons to jump/hop and start doing shit because the grounded normals are much weaker and overall less effective at stopping things. in comparison, the jumping normals are generally left unchanged and still great so suddenly 'always be hopping' goes from a joke to the actual strategy because so many characters have a better chance of stopping the opponent from their hopping pokes with their own.
i guess all of that isn't necessarily part of feel but it's the conclusion i've reached that stem from that basic 'feel' related issue. a lot of stuff tends to be connected and having that one thing changed causes all of the rest of that stuff to change, too.
like i said, i'm not 100% clear on why i really dislike kof13 but all of that plays a major part into it.