First of all, I don’t notice big differences in drop rates on different mayhem levels and between normal and TVHM. The lootsplosions are bigger in higher mayhem levels and more legendarys seem to drop but the odds don’t seem to improve much.
The feedback I read about the increased dedicated loot drops from the ‘Bonus Boss Loot’ event seemed to show that the community enjoyed the event (except that it was ending and that it took place right before a level cap increase again) and many wanted to make it permanent.
I think a good compromise would be to scale dedicated loot drop rates. M6 would give you a 20% chance to get a dedicated drop, M7-40%, M8-60%, M9-80% and M10-100%. This would make players playing in the higher difficulty levels feel rewarded.
There are enough versions of weapons, damage types, annintments and passives on mods and artifacts to keep people busy with farming even when bosses drop their dedicated loot 100% of the time. There are also enough legendary items to keep people busy farming.