OP stated from the beginning it won't work on full resisted entities (like bosses) so your whole argument about gap closer and such is pointless. If you don't think it's a useful enough ability, that's fine but I think it's a fun one that must feel good to use as tank. I'm sure 90% won't use it but same goes for other Tank abilities (arm's length) so I don't see that as a reason to avoid adding it.
1 semi useless ability really isn't a big deal imo especially for role skills, there are already plenty that almost never get used. Niche abilities are a nice thing to have imo, it feels great when opportunity arises where you can gain value from them. Nobody is forced to slot it.
Don't think anyones going to lose sleep over mob action cancellation, you can already cancel their action by stunning them.
