Adding up Attack and Defense dice roll modifiers is the player and DM spending 5-15 minutes on their turn adding together all the modifiers that tells them what their chances are for firing a bullet in three seconds.
5-15 minutes??!
What?
Are you nuts?
At most you're looking at vision, movement and / or distance penalties.
Movement penalties are fixed, so you either get it or you don't.
AR's change with range so that was not "simplified away" but actually made more complex because now EACH weapon has it's own AR varying differently at range rather than a fixed range modifier.
At most it would take you about 60 seconds to look up your vision penalties.
Geeze if that's the basis of the change from modifiers to AR and DRs then no wonder 6e is so....nuts.
It jives with my 5e experience.
Yes, it takes a looong time to resolve stuff because of the amount of page flipping and rule hunting.
Maybe you've got range penalties memorized. What about the
increments? Gotta verify if 50 meters is the top of one band or the bottom of the next. And it's different per class of firearm.
ok, maybe you've got THAT memorized too. Or you have a GM screen/cheat sheet with that info handy and it's relatively quick to resolve. Even if it only takes say 5 seconds to verify, over the course of a single combat pass that can be a minute right there. Stuff adds up. It really does.
And that's the easy stuff, that you know both A) has a modifier and B) where to find it. Stuff invariably comes up where you're not sure if you remember it's covered by the rules or if the GM will just have to wing it. Obviously, every second spent hunting for something that doesn't exist is a wasted second, when the GM ultimately just makes something up anyway. For example: in "this one fight this one time" I was the GM, and I was convinced I read somewhere that when you spend a Take Aim action to reset your recoil counter, you don't gain any other benefit from that Take Aim. When I informed the players of this, they unanimously agreed they never heard of such a thing (which they always do, even when they know damn well otherwise) so we consult the books. I can't find it, after however much time I spent before realizing we're wasting way too much time, and I just decide to ignore it and move on. Time sunk over a very piddling detail. In this case, a detail that doesn't even exist anymore in 6e (recoil).
And then there's the stuff that absolutely is covered, but isn't relevant most of the time. Maybe this game has a decker who wants to do combat bricking. Usually noone bothers because of the shit action economy, but today the player doesn't care. Trying it anyway. Time to break out another chapter of the book entirely. Look up matrix spotting rules, because that's never been satisfactorily explained anway. GM's gotta now decide how the matrix security is arranged, because NPC PANs have never, ever been codified (that I've ever seen, anyhow). Etc etc etc.
Maybe the magician is trying out new drek today. How does critter power X interact with this combat? Flip to a new chapter. Review a critter power entry. Think. Rule. Oh, never mind that answer, let's go with this spell instead. Break out another splatbook entirely. Etc. etc.
Combat goes super, super, super slow in 5e. Granted some of that stuff is edition agnostic (invoking seldom used rules, splatbooks) but 6e streamlines where it can, and I think that's a BIG help.