Counterpoint, Tera Blast is a conditional Hidden Power that commits a valuable resource for 1 good STAB coverage AND a moveslot that may or may not be good in that match. Of the 2 mons it was arguably Broken on (3 if you count Espartha), 2 were set up sweepers and the third (eleki) had an incredible stat spread that could be physical or special depending on build. The only reason Eleki was broken is because it had near perfect coverage with switching options thanks to Volt Switch, Bolt Beam is just that good. But you also don't see Jolteon or Raichu taking up the mantel of Regieleki because even though they can do the exact same thing, their stats aren't as good.Tera Blast is effectively twice as powerful as Hidden Power and could also be run as a physical option. I'd say there's a big gap between the two.
Hidden Power is better in every way IMO because you get an immediate pay out without committing your tera, which is an insane resource. The only reason Tera Blast was broken on Esparthra, Eleki, and Volc was because they either had godlike set up or godlike stats/abilities/moves that worked with Tera Blast. Otherwise, if you don't tera you get a base 80 normal type move.
The majority of the best tera users in the tier don't even use tera blast, and of those that could they often don't because they have a better move that has a secondary effect, even if it's weaker, to match said Tera type.
Except that doing so basically means a hard commit to using tera on that mon for Tera Blast value. And if you don't then you have a bad normal move that doesn't really add to your ability to KO mons. Look at it for what it is, a move that is good based on the mon using it. Volc was good because it had Quiver and already great coverage. Tera Blast fit well because it could handle any threat you wanted by swapping out one of it's other moves.If tera blast was banned then volc probably wouldn't be. I agree with you that it's basically a non-issue, but some mons definitely use it all the time.
I'm a pro tera player through and through, but the reason this doesn't work as an argument is because the move itself is Pokemon dependent.To borrow from another player I remember reading on another thread, it's the Smeargle argument, Can Smeargle be oppressive if it has this move. Baton Pass and last respects could be insane, as could shed tail if Smeargle can get it off. But Tera Blast? Nah.But like, why though. Why suspect the whole mechanic when most of the big losses in terms of bans are because of terra blast. If we can do team preview+ban tb and retain all the mons that we'd retain anyway why not do it?
I'm in the Pro tera camp and I would be fine with a tera preview, although it wouldn't be my preference. However lets ask ourselves this... Volc has been a Thorn in OU since gen 5 and has only gotten stronger as the gens progress. Quiver Dance is just that good on it. And in Eleki's case, the only reason it wasn't banned last gen was because Hidden Power was removed. HP Ice Eleki would have disintegrated gen 8 OU.