not gonna fully reply bc i wanna save a longer response for a policy thread. the other threat in question would absolutely be dragonite, i doubt its a contentious point whatsoever that what its doing in the tier rn is pretty absurd. thing is, dragonite will absolutely score significantly higher than tera blast considering yenno, its a physical pokemon. problem is if you look at the surveys as purely data and not a wider picture in this scenario, you are suspecting dragonite first. the tera blast "problem" is a wider issue that you can't get a proper conclusion on from a survey, hence a policy thread. the move has been pushing strong sweepers over the edge pretty much the entire gen; volcarona, moon, goug, whether they are still broken without isnt relevant, the variety of sets the move has provided to these have pretty much been the nail in coffin for all them. the last survey was before dnite really started to become the "i lose if its the right set i just lose here" mon it has been since OLT. suspecting dragonite first because it scored significantly more than tera blast without establishing what the plan is with tera blast first is absolutely a mistake, its not unlikely that something(s) similarly annoying will take its place anyway, nor does it acknowledge the root of the problem properly since you have to make a decision on if its banworthy in the current meta and not theoretical situations (which if we ban tera blast later its going to be even more of a pain in the ass going back and re-suspecting since theres no content drops for this generation left that can act as soft resets). reading data alone from a survey doesn't fully give context to this particular situation, especially given the variaty of people we poll, unclecharizard83 may think dragonite is too much for the tier but also not understand what the problem is on a deeper level.
the last thread also suffered from "how can we fit this into our current policy" opposed to looking at the moves history and adapting the current policy to give a better conclusion on how to move forward. the beauty of being a non official competitive scene for a game is our ruleset can and should be adaptive and given how gen9 pushed the goal post in several regards, we've been trying to apply a older concept of tiering framework to something much more complicated that it was initially intended for.
I agree with this for the most part but I do want to discuss the specific pokemon (as well as Espathra) that you mentioned above and if/why they were problematic because of tera blast.
Regieleki: No problems with this one. This is a prime example of a pokemon being broken because of tera blast though it is arguable whether it was because of tera blast itself or the flaws of Regieleki that tera blast helped fix.
Espathra: This is a pokemon that would be broken in my opinion without tera blast but was definitely banned because of it imo. If it was allowed back in OU, it would still probably run over the tier but there is a chance that both steel types and the plentiful amount of priority users would be able to keep it at bay.
Volcarona: It is even more contentious whether Volcarona would have been banned without tera blast than Espathra. Tera blast was definitely what pushed it over the edge, but it is possible tera on its own was what made it so broken in the first place. I personally think that without tera blast Volcarona would be a relatively balanced pokemon in OU.
Gouging Fire: While tera blast certainly helped, this pokemon was already broken due to its insane set variety and snowballing potential thanks to Protosynthesis.
Roaring Moon: Whether it is broken without tera blast is up for debate but no matter what anyone says this pokemon was banned because of TB Fairy. Before the "discovery" of the TB Fairy set there was little discussion on the idea of Roaring Moon being broken as it was usually pretty predictable. It was simply another powerful dragon dance sweeper that would face competition from others such as Dragonite and Kyurem. However, at some point (I want to say a month but I can't remember the exact time) before the suspect and eventual ban, a huge wave of experimentation happened that resulted in a lot of new Roaring Moon sets being discovered with easily the most controversial one being TB Fairy. Once people realized this set was as dangerous as it was people immediately began to call for a suspect test. I personally believe that we should have waited another month to see if this set was just another flavor of the month set or not, but I digress. What is important is that tera blast was an incredibly important factor in the ban of Roaring Moon and I will come back to TB Fairy specifically later. It is possible that Roaring Moon would have been broken anyway as people started to realize you could sacrifice speed on Roaring Moon for more bulk but either way the main reason it was suspected and banned was because TB Fairy was so powerful.
Kyurem: This pokemon was suspected mainly because of its set variety but tera blast was a big reason for this variety in the first place. Without tera blast, dragon dance sets would be far less powerful as there are plenty of steel types in the tier that easily switch in and beat it. However, tera blast gave it the coverage needed to run some truly scary combos such as TB Ground who's only counter was Corviknight and TB Fire who's only counter was the (at the time) rare Heatran. I do not think Kyurem would have been nearly as scary if it didn't have access to tera blast and it already feels way less scary now that its role as a dragon dance sweeper has been more or less outclassed by Dragonite. Even with Dragonite being better in most cases though, Kyurem still has reason to be used as a dragon dance sweeper and while I don't personally see it very often I am sure it is used in tournaments enough to be a threat. Without tera blast, Kyurem would probably not be nearly as broken even if it would still be quite good thanks to its special sets.
Dragonite: After Roaring Moon was banned, people quickly figured out that Dragonite could do a lot of the same things that Roaring Moon did and in some cases it could do them more effectively thanks to extreme speed and multiscale. However, while it also uses tera effectively in general, some of its most polarizing sets use tera blast, with the most common ones being TB Flying to finally get a STAB flying move, and TB Fairy to give it some great neutral coverage and a solid defensive type. Dragonite is particularly scary because it can also utilize many defensive moves such as encore and roost to make sweeping even easier. Dragonite is already very good without tera blast but it is hard not to argue that it would be tera blast that pushes Dragonite over the edge in a suspect.
For every pokemon mentioned here (except Gouging Fire) there is a clear pattern of tera blast either being the main reason or a major cause of a pokemon being broken. While I am not sure myself if tera blast is broken or not, there is enough evidence from all of the pokemon I have mentioned as well as the other controversial tera blast users not on this list to warrant a suspect in my opinion. If not that, the policy thread should at least be reopened for discussion and allowed to be a bit more flexible with the discussion. Thank you for reading and please don't be too harsh with any replies.