With respect, OP is incorrect in 2 ways:
First, OP is ignoring all the parts of old relics that weren't doing repeated instanced content. Previous Relics always included FATES; there are no FATES here. Both ARR and Heavensward Relics contain steps where crafting and gathering were among the methods available to progress your Relic. Not here. And there were plenty of steps that required players to do a series of specific dungeons or trials, which explicitly forced variety. These are all meaningful differences.

Second, nobody was ever limited to do the same Trial over and over again; they chose to do that because it was determined to be the optimal solution to acquiring the resource. In that way, it will be no different here: an optimal solution will be found, and that's what most people will do. You've always had the choice to stray from the optimal path if you prefer otherwise.
I will say that in terms of gathering a single resource, tomestones do offer a wide variety of different ways to earn them, and in that way it does allow the possibility for different ways to farm.

But in the end I think that benefit is negated by having 3+ consecutive steps that require gathering the same resource. For most players this isn't going to encourage a variety of play, but rather means that for 3+ consecutive steps of their relic they will be doing the exact same farm. In step 1 they will choose the farm that is most optimal for them, and that's the farm they'll still be doing when they finish step 3.

If you want players to vary their play, you have to incentivize them — or force them — to do it. This was baked into the design of previous Relic quests, but it is unfortunately absent here.