This is a flaw in most pickup comparisons. If your rig is setup in a way that most everything sounds good through it, and you change guitars for flavour, then it's ok. If you tweaked for one particular guitar, and then run a different guitar and/or pickup through it, it won't complement that guitar/pickup as well as if you retweaked for it. For example, if you turn the treble down to warm up a Strat, a fat modern humbucker will sound muffled. (Not an attack on UMD; general "you"s intended throughout.)