Hello, I am one of the Organizers from DuelCircle an official fansite that hosts seasonal tournaments.

Balance within PvP is pretty tricky to get just right as it's adapted from the PvE scene where strict rules aren't needed for the landscape. The problem you mentioned where people are able to set for their opponent to gain a massive advantage is a pretty major flaw with how hard it is to counter the within a match. Having the game lock your deck and or gear would be a good step in the right direction to mitigate the problem at hand but not entirely solve it.

The reason why setting is so powerful is due to our primary resistance stat being based upon percentiles instead of a flat number. The more you have of this stat the more powerful it will be within your build as it exponentially improves in potency of damage mitigation. As it scales off an initial effectiveness of 0-100%, it can reach complete damage reduction of incoming attacks. This purposes an issue of actually getting to the win condition of defeating an opponent if you can't do any meaningful damage, which is why we have gotten means to pierce through it with jewels, infallible/flawless, shadow strike, and higher pierce from gears since Darkmoor. In theory it seems to be a good solution to have a stat remove the problematic one at hand, though there's faults. The primary issue at hand is the fact that any of these are not capped. This allows someone who wishes to persistently set against someone to just use more of that stat to either have an okay amount of resistance after pierce or go for something that is really strong resulting in your natural hits outside of your piercing windows to be pretty unrewarding. Which has lead to the natural progression of players using ward pets in the arena to have a higher effective resistance rating under normal conditions to better survive the current offensive meta. A better solution at least for competitive play is to have a cap/cut off point where your resistance only counts for so much, say 70% for resistance and 30-40% for piece for an effective resistance of 30-40%. This is what we do for our seasonal tournaments Christmas Clash and Luau and so far helps to even the playing field against overusing stats.