He's no great shakes. BUT he's an experienced lineman who has started games. In a more limited role, I'd rather have as many experienced bodies as we can.
In 2018, Colin Byrne [who'd started games] got demoted to the second unit, mainly due to Roberts returning from injury. In the FSU game, Evan Adams got tossed after an altercation, and we slid the experienced Byrne in at OG. Byrne wasn't as good as Adams, but it was nice having an experienced player to lean on in that situation, and there wasn't a big dropoff in that game.
Not a huge Tisdale fan, for the reasons you specify -- but we've had so many injuries, etc. plaguing OL, I want as many options as possible -- let the coaching staff figure it out. And if Tisdale has truly been lapped by better options, then that's another sign that OL depth / quality is improved.