It was 150 cw, vacant belt against marg, so those facts alone make it illegitimate, together it's 100% useless and shouldn't be any more recognized than a usabfabcjrbsfake title
No, and neither did Manny because he vacated it and said that he would never fight above 147 again. Floyd's 154 belt wasn't either as he fought for it at a catchweight and didn't bother defending it once. The difference, though, is that Manny vacated his belt while Floyd held his hostage.
If you consider Canelo the lineal champion at 160 then I'd say you'd have to consider Manny's 154 title legit as well.
the fight was legit 154. they made the catch weight obviously to even the playing field but their fight night weights are still a huge difference. it's not a lineal title but the organization gave the title so it's legit. not defending it is totally different matter.