Gaea's definitely more powerful than Odin. She's some kind of incarnation of Earth itself, whereas Odin is just one of Earth's many gods. Regardless, we've never seen anything to indicate that the classic Thor was more powerful than Odin. Odin is portrayed as wildly more powerful than Thor pretty consistently in all things but pure, raw strength. Granted, Thor still wasn't on Odin's level after he inherited the Odinpower. I think that reflects your argument about Thor's potential being greater but his ability to harness it being less. We saw as much in "Ragnarok" when Thor finally goes through the trials Odin did (more or less) and gains the wisdom and knowledge Odin had, resulting in Rune Thor, who's easily the most powerful incarnation of the character ever. Probably the most powerful god character Marvel's ever had, too.