Armstead, Brown, and Smith aren't Bushrod.
You don't know that. They could be better than Bushrod. Bushrod isn't all that great. He was solid, but not special.
Brown has played well when he got PT. He's just had injury issues.
Smith has the talent, he just hasn't been able to put it together. I posted in another link about OL who are drafted high, become a bust, but after time actually go on to have average careers.
Armstead is a gamble... But our gambles on guys like Evans, Bushrod, DLP, Strief, etc., etc., etc., on the offensive line have worked out so far.
If you are really this worried about the LT spot, you must stay up at night with nightmares about the Saints defense.
Oh yeah, you aren't a Saints fan because you still think our LT is more important than our guards in our offensive system.