Well, Disarm has been a published rule since the DMG came out, and there is no shortage of ways a caster can lock down a fighter. I'm still not seeing this as any kind of unbalanced caster nerf.
To lose the spell, the fighter in my analysis would have to recognise that a spell was being cast and hit with his attack, and the caster would have to fail its concentration check. That's a whole lot of "if." In the overwhelming majority of cases, a combatant would be better off taking his regular turn in combat and saving his reaction for opportunity attacks or a class feature. I'm certainly not, as a DM, going to waste one of the few rounds of combat a minion typically survives holding a Ready action to make an attack, hoping to get the trigger and make the shot just to deny a single spell from being cast. That's not a good strategy. If you're planning ahead, blocking an enemy caster's vision is a much more reliable way to protect the party from spell attacks, and much more easily accomplished.
"Well, Disarm has been a published rule since the DMG came out, and there is no shortage of ways a caster can lock down a fighter. I'm still not seeing this as any kind of unbalanced caster nerf."
Yes but disarm does not end an action, just an attack. With typical interaction rules a fighter can draw another weapon and continue fighting. You interrupt a rogue or caster - not do many options (rogue might get to use TWF if a lenient GM rules being disarmed before you get to attack still counts for enabling TWF.)
As for wizard bring able to lock down fighters, sure, that was built-in and tested. That's part of the many reasons wizards have d6 not d20 HD etc.
Now we are talking about adding in some new mechanics to that mix.
But, the fact is this, it's not really about fighter vs wizard. It's more about a mage, a guard Captain and six thugs against a group. In that case, a couple thugs being able to knock out the caster ability to cast makes a big hit.
But your focus on the fighter vs wizard ko vs each other... kinda seems like the goal may be more aimed at the casters and in games where it's a problem, hey, house rules to make frustrating the casters easier might be very effective in discouraging their play.
I would, myself, in a game with ever growing interrupt rules, go for monk myself.