It's really not substantial. Substantial is the old pvp armor would for my class had well over 400 magic damage less than pve t4. You only had the damage rings and no dps version of a pvp cape or neck, the weapons were a joke. The t1 gear was absolutely trash until they rebalanced it. If you don't remember, it had ZERO critigation or tenacity, and extremely low stats on almost everything but constitution and protection.
So, compared to what the armor USED to be to now, it's actually very nominal between the sets. Of course t3 is going to be better, but saying you can't be competitive in t1 on any class just is not simply true. Your figures are deeply overstated, since the majority of the magic damage difference is from the lack of a dps cape and neck, which is a huge amount. The actual magic damage between just the armor sets is hardly noticeable.
Everyone agrees there should be a t0 set, I have suggested it many times throughout the years. But with the pvp week on both servers, continuous quests on fury, and the new vanquisher quest, it's extremely easy to level now compared to any time in the game. It's the easiest it's ever been, I really don't see what your point is other than there isn't a t0, which you could buy t1 outright in the store, if you really wanted to.