This has been the complaint against PvP tamers for ages, not just on Siege, Smoot. The Dread example fails an equivalency test because you'd need taming to "loot" a Dread and I'd need no Swordsmanship to loot your weapon. A sword can be replaced. A Dread cannot unless another Vanguard Invasion comes along. And, in practice, it really doesn't work that way. You'd take out the "naked" tamer, avoiding the Dread. And were you to die to a "naked" tamer it would be shame on you
PvP is a game of mobility, constant mobility in a way PvE is not. And pets are not terribly fast in attack mode. Your tamer opponent would need to dismount you first, something he can't do with his pet unless it's a Hiryu which cannot move as fast as a mounted opponent no matter what its stamina is.
Still, the entire notion of tamers in PvP inspires EXTREME emotion. Before the logout rule was in place - the bit about your pet logging out if you do - people would go to elaborate lengths to either loot or remove the pet. One fellow used to aggro pets of fallen tamer foes, get them onto a boat or simply far, far away from the tamer until they'd go wild.
I simply gave up on it. And I'm not making a tamer on Siege to try to kill people with pets. And if rule set inconsistencies were show stoppers I wouldn't be able to play on any shard