The higher-end ones could take out most High Metas. Megatron is powerful and durable enough to take out all but the most diverse of that group. And depending on the writer, his cannon is capable of firing black holes and/or anti-matter, which would seriously f- some people up.
But your standard-issue Transformers, that aren't gigantic, morphed, or uber in some way, are probably floating right around low meta.
It also depends on the transformer. A lot of transformers have meta abilities and powers similar to mutants. For example, Autobot Windcharger has magnetic powers.
Their standard weapons (which are fair game in these threads just like Thor's hammer is) also have some insane abilities.
A decepticon like Predaking would make mincemeat out of most non cosmic powered opponents.
a full scale assault on earth by all the decepticons that megatron/galvatron commands, and the ones on cybertron under the command of shockwave would be worse imo then the skrull invasion X2. and that's being generous.
A few hundred mid to high metahuman level villains would overpower Marvel Earth? Is it that weak, really now?
A decepticon like Predaking would make mincemeat out of most non cosmic powered opponents.
Comicwise isn't predaking's only feats wearing Optimus down enough to be beaten by Megatron and in his second appearnce being one shotted by Megatron.
Predaking only had one recorded win. Against Brutiucs in the dreamwave comics.
His strength is also only listed at 500 tons.