I think we need to wait more time to start thinking about ranking Gatr.
As much as I love it, Gatr has a lot of flaws. It has really heavy 4MSS, thus getting check'd or counter'd by a large amount of things. Azumarill, Rotom-W, Keldeo, Gyarados, MVenusaur wall its entire coverage alone and thats just the most relevant ones, without taking into account Alomomola, Quagsire and friends. If it lacks fighting coverage, Ferrothorn walls it, if it lacks Ice Punch MAltaria, Chesnaught, Tangrowth and Amoonguss wall it, if it lacks Crunch Slowbro says hi, and if you lack Aqua Jet you're going to be revenge killed fairly easily when using a DD set, because lets be real, Gatr has small amounts of chances to set-up, and when it can, its just easily checked. My problem with Gatr is that it lacks a secondary STAB move, and therefore it can't really damage everything it wanted to. Yes, MGyara lacked a secondary STAB in XY, but MGyara had Mold Breaker to break would be checks/counters to it such as Quagsire and Rotom-W, while having intimidate pre MEvo so it had a better chance trying to set-up.
No matter what Gatr does, it's going to be stopped by something on every team. This doesn't mean it shouldn't be ranked however, its just that there hasn't really been enough time for us to realize what is the best set for it and we should therefore, wait a few more weeks before nominating Gatr.