I actually think it's better to have more variety for failure and success around everything except attacking. At the end of the day, every martial willattack, and every caster will cast, but there can be ways to make it much spicier. What you suggest, for a magic equivalent, would be a crit fail or succeed for casting an offensive spell. That'd be bad. It's why most fumble rules suck. It removes too much agency.
What the Fighter has by way of reactions and AoOs is what a Wizard has by way of counterspell: a specialty in a "common" field (Spell and steel are mundane in DnD). For a Goblin attacking a Paladin, an attack pinging of the shield rather than the armor is the same, but only a Fighter can make it a two weapon parry. That's the kind of "nice martial/mundane thing" people have wanted. It's a layer only the best can access, and no dice luck or spell can mimic it. It's a design decision I'm seeing with a lot of things.
Offensive spells do have critical success in 2e, they deal double damage like martial attacks. At +10/nat20.
I also don't think it effects player agency, but that's an odd aside so maybe? Many hundreds of critical fails will occur for the enemies in a campaign. Moreso with the proper party now that the -10 rule is here.
Paladins are supposed to be the Defensive class per one of their earlier blogs, so maybe they'll have something more along the lines of what I want.
I still don't think at high levels a single reaction is even close to okay for martials. As has been said much better for 14+ years, if casters can aim for a much stronger Prince of Amber, why does the fighter not aim for Ares?