Do employees suffer from having too many jumps in their Resume? After some time, companies would be less inclined to hire these people right?
The only time this would maybe not apply is director/VP level roles, though if you're switching at that level you presumably have a pre-existing relationship with someone near whatever role you're trying to move into.
Fuck HR. 12 months is nothing for actual deep learning. I've seen job hoppers come through my company and it's obvious most of them don't get very deep in the work and just move on instead of becoming a real expert in the system. It's one thing not to hold it against them, but it's something else to say count it as an advantage at such short intervals.