Both ways are fine in my eyes, if a small group can take it down then cool, if the big groups find it and kill it then also cool. It's an open world mob so people have free reign to do what they like.

I personally prefer the huge hunt group we have on Excal, but if we come across a normal group attacking an A rank we stand back and let them fight it. If they die then we will engage, or if they've done a fair chunk of damage already we will engage. But nobody will ever complain about the small group claiming it first.

the simple fact is: you either make it to the mob in time; or you don't.