Yeah but you're comparing apples to oranges. And i'm not just talking about Vaizards to Arrancars. These arrancars were nothing special in terms of power before becoming arrancars. They were not Vasto Lordes which would be the most powerful incarnation.
However the Vaizards are. They are from captains and Lieutenants. The most powerful rankings of Soul reapers.
If Ulquira had a 2nd release this tells me we haven't seen the extent of what a true Shingamification is capable of. There is no telling what a Vasto Lorde who goes through this process will be capable of.