Feats and statements are proof of something, solidifying or implying what we know of the character's abilities. Without such, a claim would be fairly baseless. This is apparent in the case of GT > Super. One has both feats and statements of characters being MFTL+ and capable of destroying the universe with the combined power of two top tiers, whereas the other has no statements to place them above Multi-Solar System level.
The one prevalent fact is that neither feats nor statements give anything in GT's favour. I'd honestly like to know what it is that people use to argue in it's favour, as right now, I'm seeing no solid evidence to place GT anywhere close to Super. To ignore feats and statements as comparison due to them being different continuities is essentially ignoring the entire concept of fictional versus debating in general.