It's entirely true that if you value overall group effectiveness, efficiency, and progress above all else, healers are going to be the absolute last to get their Sands and Oils. That's pretty much an undeniable fact, due to the very nature of healing versus damage (and arguably even healing versus tank survivability).
And it's also entirely true that if you value distributing rewards equally more than you value group effectiveness/efficiency/progress, this problem is easily circumvented by just giving healers the same chances as other roles for casting lots on those upgrade items.

But there's no good reason whatsoever why a group should have to choose between min/maxing their group progress, and making sure that all members of the group are receiving regular rewards for the time and effort they put into the group. Awarding one Oil or Sand to every player in the party would ensure that nobody has to make that choice, and would still not trivialize progression, as A) Sands and Oils can only be used to upgrade equipment that is already under the Soldiery lockout, and B) Are only obtained from getting deep into the Second Coil, meaning that nobody is receiving something they "don't deserve" and everyone who gets them has completed much of the most difficult content in the game.