Also Smeargle sucks.
I'm going to get shit for saying this, I already know.
Lets get real here, Smeargle does suck. I'm going to use your quote smoothly segue my way into an argument for why Smeargle deserves D-Rank.
So Smeargle is unique in that it gets every move in the game, which is an excellent niche, barring the fact that its stats blow and force it into the role of a suicide lead, which as we know is pretty much a dead niche since Gen V. Sneargle lacks the bulk to take hits, and doesn't have the offenses to use its massive movepool to its advantage, which forces it into using its acceptable speed and running a support set, taking advantage of access to moves like Spore, Sticky Web, Shell Smash, Baton Pass, Magic Coat, and whatever the hell else floats your boat. However, almost all of Smeargle's sets get brutally shut down by Taunters unless they run the rare Magic Coat, Spore got nerfed meaning that Grass types have nothing to fear against Smeargle and setting up on a sleeping opponent isn't as reliable as it used to be, Defog and Spinners like Excadrill and Mega Blastoise make getting rid of hazards quite easy and turning the battle 5-6 with a single turn, and finally Smeargle is forced into running a lead set with Focus Sash to avoid hazards and being vaporized later on. This makes Smeargle extremely predictable and most well made teams will have at least one way of dealing with it. Moreover, Smeagle is outclassed as a lead in the presense of Deoxys S and D, both of which are faster, bulkier, and can run a variety of sets that make playing against them much more complicated. Smeargle can carry Sticky Web, but it gets ouclassed by Galvantula, who can threaten opponents with Compoundeyes Thunder, Bug Buzz, and Volt Switch, and even freaking Swadloon, who is bulky enough to take hits with Eviolite and has access to Synthesis to allow it to come in and lay down Sticky Web multiple times, and it also happens to get Magic Coat to reflect Taunts as well.
I've gone on long enough. Smeargle may have options, but a lot of those options are inferior to other things other Pokemon bring to the table. Smeargle is usable in OU, because of its movepool, but I don't see its use above D-Rank.
Also, I just talked up Swadloon's viability in OU. Feel free to take that as you see fit, in the meantime I'll be testing Eviolite Swadloon to see how far gone I am right now.