What is faster: Rolling a d20 or rolling a d20 and adding +4?
Rolling a d20.
Making the actions which are often done as simple and fast as possible. Thats the point if enemy armor cancels it out anyway then why having a +4 to start with?
because not all enemies are equally hard to hit, and not all attacks are equally easy to dodge.
A wizard stabbing a fighter in heavy armor and shield should be less effective than a fighter stabbing a naked wizard.
And one of the simplest ways to compare how strong 2 things are is by giving the each a bonus.
That said, making it 1 roll instead of 2 (attack roll then damage roll) is very much something that can be simplified.
Also as said one can also just not allow to do it. Or give disadvantage etc. To not have negative modifiets. The main point is not having to add an arbitrary number as a base.
I mean, you could add an arbitrary amount of dice instead.
Rolling 4d6 damage vs 3d6 armor for instance.
Not sure that's simpler that +mod, but yes, there are other ways to show a gap.
This is why for many people in high level 3.5 or in PF2 small bonuses feel unsatisfying "why should I spend an action to give my ally +2 to attacks when they got +30 already?"
Agree the numbers in PF2 get excessive.
IMO: go from 0 to +10 on a d20.
5e is close-ish to that.
Then another thing, even for progression modifiers are not necessarily. You can also just use levels.
Adding +level is what makes PF2 get excessive numbers.
Like "you can feel how your fast combat experience gives you and edge in this fight against these unexperienced foes" says the GM and subtracts -2 from all enemy attacks and defenses (which can be done before the fight or if its with digital tools or an AI GM directly).
D20+ (Level 5 - (level 3+10)) is mathematically the same as d20+5 vs 13 for them. Except it takes more on-the fly calculations.
Definitely could work for a computer. It would still fundamental be using mods, just display different.