I'm saying this to try and be constructive and not at all offend you personally- the issue is with the replay you chose, armaldo is not shown to do anything at all that any other rock types can't do (and even do better)- the damage from aqua jet was completely negligible and even despite getting lucky with two 5 hit rockblasts, it was still unable to do anything to Venasaur. On top of this it took an absurd about of damage from the T-Flame as it doesn't even resist it's stabs. Literally any other rock type would have given you momentum and mons like tyranitar or rhyperior have greater bulk, an immunity to electric (for rhyperior), better resistances and a greater attack stat. Tankchomp or scarf chomp are other mons that can do armaldos job better. Non stab aqua jet is nothing to get excited over, and heck, even mons like kabutops and relicanth can do this job better and they're extremely niche.https://replay.pokemonshowdown.com/battlespotsingles-294302498
Unfortunately this is the only battle with Armaldo I saved, I'll do some more with it to show why I even brought up Armaldo in the first place. This battle probably isn't the best example, since I get quite lucky, and totally mess up entering Gengar(it was a really weird set, and I never used it after that battle. Although, considering Gengar didn't get to use a single move, it's like I never used it anyways.)
The point of these viability rankings is to clearly display the utility of a Mon in the current metagame, and if it is outclassed in every roll it possess, it shouldn't be used and does not deserve a rank. The only niche I can see that armaldo has is perhaps a ludicolo check with X scissor on rain teams? Even then it takes an absolute beating from hydro pump. I really do not think it deserves to be ranked