Both of these decks having their own built in acceleration is nice and all, but unless we saw more cards for these themes I'd trust Metagross over Grimmsnarl/Morpeko.
Yes, Morpeko can reach KOs with 1 Grimmsnarl buff, but you got to commit 1 whole Grimmsnarl evolve to the Morpeko every time you want to do that, which is taxing with how tiny Morpeko is. It isn't like Gardevoir where you'll often keep Gardy in play for several turns and get value from it every turn. Grimmsnarl's attack for itself is still underwhelming, and it doesn't have a niche like Metagross has in tanking damage. Having Spikemuth for consistency is a great feat, and I can only hope that Marnie will have a wider toolbox down the road that Grimmsnarl can better take advantage of.
Metagross is straightforward, and likely will get compared as a Steel Tank against Archaludon ex. Metagross tanks bigger hits, sometimes more hits, and is less conditional on energy for setup; whereas Archa hits better damage benchmarks and is a stage 1 rather than a stage 2. The different basics also have their advantages. I don't think this would be as much of a competition if Metagross did any more damage in its attack, as even 210 changes what it can OHKO for ex's. Each of those is going to be more effective in different matchups, and Archa does lose some consistency to rotation. Worth discussing both metal decks down the road.
Energy Recycler coming back into the game is great, even if we do lose the strategy that took the most advantage of it to rotation.