I will try to sum up my arguements against DRs by Copy/Pasting a few basic ones and stitching them together into as compact a size as I can manage;
First, Diminishing Returns is something that could be over-come, unless EA/M plans to take it to a level where after certain consecutive uses potions simply do nothing. This will not be acceptable by players however.
Second, if someone reaches their DR "limit", supposing EA/M uses DR to address the issue, and the cure potion has then no effect, I'm also guaranteed to poison them constantly while this applies!
No matter how difficult you make it for a poison to be cured(unless it is unreasonably hard therefore making poisoning OPed), it WILL eventually be cured, and as this works now, "Eventually" translates into "Instantly". This is because the time it will take to "eventually" be cured by constantly drinking potions through macro-mushing, will be neglectible as there would be no timers.
Assuming EA/M would allow curing the most potent poison through potions alone, it would still occur fast enough. And EA/M would, in this case, allow even for more than just slight chances to cure the strongest poison through potions alone because I said above : If they made it too hard to cure through potions alone poisoning would be deemed OPed.
Then of course you'd have to face DRs applied to poisoners as well, and however potions work at THAT point, poisoning will be completely useless for what it requires and what it delivers.
I see DRs as an All-Or-Nothing, last resort move that will have to affect EVERYTHING to a point of rendering all affected game assets COMPLETELY useless at a corresponding point(assuming I would be using 1 GCure for 1 Infect, both assets would at the same time(and after the same number of uses) end up being COMPLETELY useless), from merely consuming food to every single spell and ability in the game, with VERY FEW exceptions. Where DRs are applied I am certain a better solution could be found by thorough examination of the issue.
Last but not least, as a poisoner would spam Infect whereas their target would have more than a couple of counters, the poisoner would be reaching their "limit" much faster than the other person would reach their potion limit even if we take into account that 1 LP equals at worst(and not in theory but in reality) 3 GCures.
It is no solution IMHO.