I've been playing DRG in high end content for several years now and I consistently hit the vast majority if not all of my positionals in every single duty I do, because I like positionals and playing for perfection.
Saying that the existence of TN trivializes positionals is the same old song that many non-melee mains use to justify the removal of positionals. It's as silly as saying that cast times are irrelevant because Swiftcast exists.
A DRG missing a RT because of a missed positional, like in ShB, would lose 350+ potency from a failed 5th hit, which happens once every 12.5 seconds at 2.5. That is almost as much of a loss as the average potency of a DRG's GCD (~400 to be precise).
No other job would be punished this much and so often without some tools to deal with them. Especially a job like DRG that doesn't get strong cooldown-based ranged attacks compared to literally every other melee. This shouldn't be taken as a call for homogenization, however, but we have to be clear with what we have.
If you actually played DRG in EW (or now but the frequency is lower in DT), you would know that you cannot control them because your GCD combo string happens all the time without interruption. So such a punishment would have to come with some leeway, as otherwise you would easily miss some unless your party was helping you hit those TN couldn't cover.
And while this issue wouldn't affect me much, it would those who play on PF or DF where, for instance, the tanks swap TBs on different positions around the boss, often rotating them for 45º degrees or more in the former or both having the stance on and thus having the boss facing back and forth in the latter.
If the loss of missing positionals was 10% or even more instead of the 2-3% that it is now, that'd be fine by me, but having it affect your resource generation for such high losses and punishment, as detailed above, would not be a good move.