Modify concentration for spellcasters to provide a higher probability of success (than 0%) vs. current damage profiles.
Currently basic attacks, let alone crits, pretty much guarantee an interruption. One would need to be a palemaster with ESF concentration and full investment to stand a chance at avoiding constant interruption.
Given the game changing nature of a spellcast interruption, this should be balanced. Here are a few options:
1) Do not consume spell slot on interruption of a spell cast.
2) Grant select spellcasters ESF Concentration for free.
3) Adjust DC calculation to change the math bringing it in range of viable skill checks (targetting somewhere from 60-100 as a random ballpark and divorcing it from the damage number could help, but needs examination).
4) Adjust how the skill check is executed changing the probability outlook based on having to fail the roll several times (or whatever makes sense)
4) Nuclear Option - Remove spell interrupt entirely, mimicking epic spells and scrolls. I'm not a fan of this alternative, but it'd be better than current dynamic.