Purge does work, but only removes briar
Which they can just put back on the gate immediately
Long story short, P/R is not a good countermeasure.
Seriously, there's videos where there are like 3-5 Rams, Tornado, Scrolls... and a gate just WON'T GO DOWN. That shouldn't be possible. Just Tornado and +7 Scrolls are like 150-160%+ dmg on the gate.