Garcia is far and away the best and biggest fighter Lomachenko would have fought. Lomachenko didn't fold against Salido, per se, even if he was shell shocked and gave up several rounds as a result. He showed heart in the last two rounds even if it was too little too late. His performance against Russell Jr. was impressive, as well, even if, in retrospect, it wasn't a tough stylistic matchup (we really shouldn't expect Lomachenko to lose an outside boxing match to a smaller man who wasn't an incredible amateur).
If they do genuinely target Garcia, that will be a big fight. Garcia was p4p on some lists before his hiatus, and his form doesn't seem to have suffered after he completely dominated and near killed the consensus #2 LW in the world in 3 rounds (and no one thinks Linares has shit for Garcia, making him the best LW in the world in most people's estimation). If Lomachenko beat Garcia, I'd probably have him p4p #1 (depending on how he beat him, I guess, and on what Ward and Gonzalez do in the interim).