If I were the Texans I wouldn't take Grayson, because I think they are already prepared to invest in Mallett for the time being. But there are other teams that need QBs and if I were that team I would give Grayson consideration at some point in the first round.
After four years with Mallett I would hope the Texans "know" they can win a Super Bowl with him, just like we knew after three years we wouldn't win one with Schaub (if you were one of those guys, even if you weren't, you "knew" he was going to require a lot of help from Foster, Aj, & the defense).
If they don't, if they think he "might" be the guy & they think that Savage "might" be the guy, I'd have no problem taking another guy they think "might" be the guy. Doesn't matter to me what round, depends on how the draft plays out to me & there usually isn't a lot of difference between a late first & early 4th round pick.
Mallett's had three years, now four of training. Savage is going on year two. If we can find & develop the next Aaron Rodgers & that guy happens to be Dak Prescott (for all I care), that would be great.
To me, that's addressing the QB position. To me, that's investing in the QB position. & that's not like these other teams that continue to throw QBs out there, each one looking less prepared & less capable than the previous.
But if they're "sure" Mallett is the guy & they do everything they need to, to help him succeed, & they're "sure" Savage can be the guy if something unfortunate happens to Mallett, then it shouldn't matter what they think of a QB in this draft unless they see a "can't miss" guy (for their system) that happens to fall to us, or within our reach.