From you other post I get it more clearly that for you this was tougher than expected. You blame the whole CR system for that, but I can't say if instead there's something wrong with the Roper's specific CR being underestimated (which is very different than saying the 'system' is wrong).
Actually, I think the encounter went as expected.
If I would do the math, it was probably harder.
I mean we are expected by the rules to do 6 to 8 medium encounters before a long rest.
I don't think we could survive 6-8 encounters with the roper without a long rest in between, because of the 20 AC and the 93 HP.
With normal attacks only hitting every 4 rounds, using non ressource attacks it would take forever to take it down. Also it can restrain everybody every turn forever, further reducing the chance to hit it.
As long as you have spells that need saving throws, you can beat the roper easily. When you are out of ressources and reduced to cantrips and normal weapon attacks, the roper will eat you alive.
So, what I'm saying is, that foe a fifth level party this was a great encounter, especially in the context of attrition based ressource management as the strategic difficulty model.
It probably used up a little more reasources than expected, but if you use the DMG Encounter guidelines, that is a rare occasion.