Galio is just weak right now. I don't think he lacks identity, he has a pretty clear one, he is meant to be as close to being a " defender/enabler from midlane" with an ability to shrug off some AP damage as is reasonably supportable by gameplay.
Preventing your team from getting run over on the entire map is obviously pretty broken, so his tools to prevent that need some clear weaknesses, eg. He doesn't turbo stomp lane to trade off for his ~semi global presence. He has a lot of CC capabilities, which also need to be compensated somewhere.
When you have galio on your team, you are meant to feel more supported/comfortable, because he could come save you/support you if you need it.
When galio was unconditionally strong (eg. think back to faker galio), it was because he could get prio in every lane and was not movable in any matchup, while having high pressure/uptime on sides.
This state wasn't particularly sustainable, so we had to give him a laning...
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