Heh. Not to steal your thunder too much, but I have said literally everything that you just said, at one point or another in the last few months.
First, there *will* be a KoLDB equivalent. It's phase II of the leaderboards. It may not come out immediately, but it will before we've got too much history. (More than a month, likely less than 6 months.)
During the "how should retcon work" discussion, the roll your own retcon idea was very popular. It wasn't even my idea, but something that a lot of players clamored for, and I ran with it as the best idea out there. I pointed out then that the only sensible method was to do brackets, which would 100% guarantee other people would be outraged by the placing of those brackets, and argue vociferously that run X worth Y mettle isn't really the same as run Z worth Y mettle, and it's not fair (or not balanced) that they're in the same bracket. I said then I'd do an advanced, searchable system at some point, but for the base brackets people were just going to have to accept that inherent inequalities exist, and if they care to be more specific they'll have to tune their searches instead of me tuning the leaderboards. In my memory this statement was met with apathy and/or silence for the most part, but I could be wrong. I've got a small chip on my shoulder (not directed against you, Nardo, just in general) that despite having already acknowledged all these limitations ahead of time, since then a swarm of players have "discovered" this same issue and told me the various ways in which the system they wanted is broken. (Sorry if I sound grumpy. I feel like I've been fielding a lot of this in various ways over the last few weeks. I expected some, but there's been a lot more, some of it about things that were obvious enough I pointed them out more than a quarter of a year ago, but nobody considered them a problem until now; and of course now it's urgent to fix, despite the relative youth of retcon.)
I don't think it's a good idea to have much greater bracket sprawl (excluding perhaps some class-based divisions) -- definitely think it would be confusing overkill to try one for each named type, and it'd only cause outrage for anyone who has a favorite run that's not one of the named ones. I'd rather leave it to the KoLDB-style outcome, where if you want to search runs with less than 5 skills using restrictions P, Q, R, and S, you can do so.
In a general sense I see the leaderboards as a mini game within the greater game of TH. As such they have their own rules and ways to optimize them, as predefined mini competitions. They will reward certain behaviors, but aren't built to reward *every* style in which people will do runs. For instance, if you want to compete in the highest bracket, doing Maso simply is NOT going to be competitive. This doesn't mean Maso needs its own board. It means if you're doing Maso, it's because you want to do Maso. If you want to be on the leaderboard, you pick something in that bracket that lets you go faster.
By providing four brackets I've tried to present some flexibility for players who prefer different play styles, but going beyond the system to cater to *every* play style just isn't going to make a lot of sense, except via the KoLDB-style "roll your own" leaderboard, to match the "roll your own" retcon system.