Basically everyone agrees that maps with more competition should be worth more to wr/tt, it's just that that's hard to quantify. Nerfing offclass times is just a somewhat accurate heuristic that can be applied without much subjectivity; I don't think anyone actually thinks that mapper-intended class is the proxy for a map being good to run.
For example, soldier times on haze are at least as competitive as demo times, and demo times are more competitive on deserted. Overall though, most offclass runs are much less grinded since not many good players want to run triplepre/wallpogo. In most cases, nerfing offclass is fine at least outside of top 3ish.
A solution that captures this would require substantial work to determine how much each map should be worth (not to mention courses+bonuses), especially since it would be prudent to do it by some kind of ballot process instead of just having admins decide. That's a lot of work, and a moderate offclass tax is better than the current state.