Tactics for playing against Sylvan.

I thought a mage hero, like Geralt, would primarily aim to do that in any scenario. And just like Phoenixes, they would be the first to attack the Priest or the General.

I would say "desirable," because you can really "fail" at this task. Of course, it would be good to get rid of the enemy hero(es) as quickly as possible, but I don't think it's a good idea to throw all your available forces into doing so.