Honestly i think the counter should stay. It’s one of those things that give the creature its identity and make It special. While It can be a point of imbalance, It only becomes a problem when combined with everything else, so If a trade is to be made I’d prefer to keep this ability and nerf other things that i believe are the fundamental cause of It being unbalanced.
The counter does indeed add more bulk to It, like you said, but it’s not the reason for It being able to kill fierce dinos. The main reasons would the higher than necessary damage combined with the fact that many fierce dinos lost vulnerability resistance on the previous update, along with the high speed. And it will only kill them when set up. Otherwise the counter doesn’t heal enough to prevent a fierce creature from killing It in 2 turns. It is naturally faster than what many people are willing to boost their fierce, so nerfing the speed is probably a must since then people would need to make the choice between faster than most boosted fierce but less bulk/damage and slower but bulkier/higher damage builds. As It is it just needs hp and damage boosts and it’s good to go against against a fierce when set up. I think 114-116 would be enough speed for It, 128 makes the boosting a no brainer, an optimal build with no sacrifice. It also has too much damage for something that has devastation, so that’s a point to be addressed since that along with the high speed(due to little to no trade off in boost builds) allows It to kill fierce dinos.
Nerfing the armor back to 40% instead of removing the counter would also be a possibility to lose the bulk.
The cleansing decelerating impact and the pin resistance are more obvious points of imbalance since It directly counters fierce, so not much to be said here. The vulnerability resistance is another unnecessary thing just gives It an edge against other resilients when It doesn’t need It.
When It comes to the counter, you can either remove that or nerf the stats(hp and armor). Any of those 2 things would probably serve the same end, they’re interchangeable in that regard. It’s a matter of preference, and i personally would prefer to keep the counter and just nerf the stats. I’d hate to see another creature lose a cool ability If there’s another way to balance it, just like what happened to tryko when It lost the old resilient counter.