I believe the best fix to this would be to make potency and tenacity more or less equal.
When tenacity = potency it is a 50/50 chance to resist.
There should also be a ceiling to tenacity just like there is a floor.
All debuffs have a 15% chance to be resisted.
All debuffs should have a minimum 15% chance to proc.
Additionally, tenacity up and tenacity down should function the same way speed, evasion, offense up/down all work. It should be based on the indivisible toon's stats.
It is ridiculous that a toon with 0% added tenacity can resist all debuffs simply because one toon grants the squad tenacity up.
I used to run EP lead with TFP. TFP would inflict tenacity down and I would STILL have toons resisting debuffs multiple times.
That just shouldn't be so.
At least not when tenacity up is a garuanteed resist.
No other mechanic in the game functions like this and it is garbage.
My RG has 98.35% tenacity and gets hit with ability block, buff immunity, shock, healing immunity all in one battle, yet a little green midget makes it so absolutely nothing lands on my squad all with potency ranging from 40-60% for my average toon.
Examples:
25% tenacity vs. 25% potency equals 50% chance to resist.
25% tenacity vs 50% potency equals 25% chance to resist
25% tenacity vs 65% potency or higher equals 15% chance to resist
50% tenacity vs 25% potency equals 75% chance to resist
65% tenacity or higher vs 25% potency equals 85% chance to resist.
With both a floor and a ceiling on pot. vs ten. it will actually matter how you mod your toons.
Far too many people mod for speed or crit chance or offense and completely ignore potency and are still able to consistently land debuffs.
That's like having your cake and eating it too.
If I've worked to get my taunting tank modded to 100% tenacity it shouldn't only make a 5-10% difference between leaving it at its natural 25-35% tenacity.