Now remember that all healers that have a crit chance over 5% are Posto (not a problem), Tryo (not a problem) and Tenrex (may be a problem).
Tenrex alone isn’t a reason to not let this change happen. If he would be too strong with a chance to heal critically (but he probably wouldn’t), then nerf his stats a bit for exchange.
Now the rest of healers have 5% crit. It means in arena the chance for this to happen are minimal. Even if it happened, it’s still only 25% more powerful heal. This happens with literally every damage ability so it really wouldn’t be that bad.
Because as I said, it’s not meant to change arena but raids. Buffed crit chance would let this change shine. It would help us all in raiding. Is a 5% chance to heal slightly more in arena a too big price for that?