Last year Houston had essentially an average offense across the season, ranking 14th in offensive DVOA, despite featuring a rookie QB, rookie OC, rookie WR2, and an offensive line with perhaps the worst injury situation the modern NFL has seen
The passing attack was #3 in explosive play rate, but the rushing attack was ranked #25 in success rate. Obviously the offensive line issues are the primary culprit with the poor rushing success rate, but I think having a below average RB1 (albeit one who surprisingly surpassed most of our expectations) in Singletary and a RB2 who was a terrible fit in this offense in Pierce. Houston potentially significantly upgraded RB1 with Mixon (if his quad strain ever heals), and they potentially also upgraded RB2 with Cam Akers, whose entire NFL career has been spent in zone based offenses, and rookie Jawhar Jordan who's an excellent zone runner
If the rushing success rate improves significantly (even getting to average around #16 in the league) would mean easier passing situations for Stroud, and also more opportunities for explosive passing plays since that should mean more plays in general since you'll be converting more first downs
With the Diggs addition, who I think will help particularly with chain moving, I think Houston should be a lock for a top 10 offensive DVOA, and I'm predicting a top 5 finish in that metric assuming average injury luck