If capacity was the overriding factor then Neville wouldn't have said utd don't even have a stadium that gets to the top 10 in the country.
Fwiw I agree it won't be the best the country but I feel you're taking the point too literally. What it means is it is up there, it's a facility of a high standard, it gives the players a sense of excellence to enable them to perform to their very best. If you compare the changing room in BMD to Goodison you'll see how much a giant leap it will be, they'll have their own warm up track, much better and bigger hydro equipment etc. Just like if you put on a smart suit it can elevate your persona this is merely an extension of that.
Finch Farm is up there, so is our HQ within the Liver Building, Goodison is the odd one out that feels it is built for the 1960-80's footballer. Neville is kind of saying that about OT although least that gets into the 90's.