You're absolutely right about what we need -- in all of the years of our decline and fall we have managed to go a grand total of one season (actually closer to half a season) with such a player even theoretically on the roster. And Tag was overweight, mediocre, and a year from retirement. The connection to our perpetually weakening defense and annual bottom 5 appearances in interior defense could not be stronger. Yet it never gets addressed. But unfortunately none of the above really satisfy the requirement -- can't help from the end of the bench.
What those guys ARE, or should be, are the 5th bigs for a team serious about defense. If you are one of those teams, you'll have a big defensive stalwart somewhere in your Top 3 bigs, but then you'll have another down on your bench as insurance too. We have neither, and with May and presumably Brockman, we have (shocker) decided to go short and groundbound again with our 4th/5th bigs. Since none of the guys you mentioned are good enough to be true rotation #3 bigs, and the #4/#5 spots they would normally fill are already taken by stubby guys, I'm assuming those guys are off the menu. The only question at this point is whether we will spend the assets to bring in a true defensive #3 big or not. But Hunter, Hollins et al are not at that level.