I'm not saying the Bucs are going to be great by any means, but there's definitely a lot of talent there. The reason Winston was under duress was because Arians' offense takes a long time for plays to develop. Depending on whose opinion you value, they ranged anywhere from like 7th-17th best pass blocking team in the league last year and it should be better this upcoming season assuming they actually take one of the tackles. Basically every position group on the team played well last year with the exception of the RBs, K, safeties and the extremely uneven play of Jameis.
I think the major question if Brady signs there is how smooth the transition is offensively. It's not a guarantee that it all clicks into place just because he'd have great pieces around him; those pieces were playing a likely very different style than what will be required with Brady. The other major question is how much of the defensive play was a fluke or not.