As you said, because default trust is "broken" then adding a report to default trust doesn't make sense.
Well I don't know if "broken" is the best term to describe the state of the DT system, but it's definitely a fragmented bunch among the DT1 and DT2 members. Some are active in tagging members who need tagging, some don't, and some haven't even been active doing anything here for quite a while. Then there's the disagreements and bickering and so forth--so the type of report button suggested in the OP is definitely not going to function well.
Exactly. I don't monitor that section much, but I think some DT2 members do and they tag scammers if the accusation is presented with convincing evidence. I negged a couple of members recently but had to remove a neg because it looked like the guy was trying to make good on what he owed but couldn't locate the accuser and didn't expect someone to buy something from a very old sales thread. Anyway, that section
should be monitored by DT members, but I think it's gotten inconsistent lately. I could be wrong about that, but I've seen some accusations with evidence where nothing was done by DT members, so it's hit-or-miss.
I do my best to tag account dealers; Vod's been covering the lending section for years; actmyname and Lauda (formerly DT) had the merit abusers for a while until that went out of fashion; not sure who's got the actual crypto-scammers covered because I don't check who gives what feedback much. Suchmoon, LoyceV, and marlboroza I think. I'm not sure how active DarkStar_ is with handing out negs. Who am I missing? Honestly I have a custom trust list and am not even sure who's on DT2 anymore.
Edit: Cryptodevil is another DT2 scam hunter, but he works in sections I have blocked. I think he's pretty active along with xtraelv, who isn't on DT as far as I know.