A correspondent writes to ask about superior, having heard someone say Federer is so superior to the rest of the field and then He is very superior. Are these acceptable? He adds: 'It seems to me that it has something to do with whether superior is a comparative form or not. I asked myself whether one could say, He's so better than the rest of the field and concluded that one could not. So I took it that so can't modify a comparative. Then I asked myself whether one could say He's very better than the rest of the field and found that this definitely sounded wrong. So I concluded that very can't modify a comparative either. But then I couldn't work out whether superior was a comparative or not, and so I could not tell whether so superior or very superior were OK. It seems to me that one can definitely say He's far superior to the rest of the field (compare: he's far better...) and also: He's so far superior. But then one can't have far with a non-comparative (compare: He's far good). But what about so on its own modifying superior? Does that work (as it would for a non-comparative: He's so good) ? Or does one need far (or much) between the so and the superior: He's so far superior?'
I quote this at length because it is an excellent example of how to explore a usage issue. My correspondent is developing a real sense of the complexity of this area of grammar. And it is complex. We are, to begin with, dealing with a group of Latin derived comparatives which don't work exactly like others in English - senior, junior, superior, inferior, prior, major, minor, anterior, posterior.... They have been called 'implicit' or 'absolute' comparatives (though the latter term is not advisable, as it conflicts with the general use of 'absolute' to mean the basic form of an adjective). Their main distinguishing feature is that they don't work like normal comparatives in being followable by than. we can say X is bigger than Y but not X is superior than Y. They are, then, comparative in meaning, but not in syntax. (Some verbs are comparative in meaning too, incidentally, such as exceed and diminish.)
Premodification of comparatives is also quite tricky. They are usually preceded by amplifiers, such as (so) much: X is much more difficult than Y. Others include somewhat, far, rather, a good deal, a damn sight. Intensifiers which work with the absolute form of the adjective won't work for the comparative: we can say X is very good but not X is much good. And conversely: we can't say X is very bigger; it has to be very much bigger.
If superior is not a true comparative, then, it won't work in exactly the same way as other comparatives with respect to the kind of modification it accepts. Because it's midway between absolute and comparative, we find both patterns in use, depending on how people think of it: I've heard both X is very superior and X is very much superior. Hence, you will find Federer is so superior... alongside so much superior.
I would thus expect to hear all kinds of mixes in the way these words are used with postmodifying constructions. Like my correspondent, I've heard such sentences as X is so superior to the rest of the field and X is very superior to the rest of the field. And there are signs of a construction with than emerging. It's not one which is grammatical in my idiolect, but you'll find on Google such constructions as the proposal is far superior than the current system and suchlike. I wouldn't be surprised to see this becoming standard one day.
But all of this is in the melting pot, now that the use of so has altered. Today we hear it being used with nouns and noun phrases, with strong stress - That is so 1960s, That is so Marks & Spencers. People who do that are not going to think twice about He's so better than the rest of the field. The usage isn't especially recent - the OED has intensifying uses of so going back to 1913, mainly American - but it certainly has taken on a new lease of life in the UK in the last decade or so. Because the Latinate adjectives also have nominal function (e.g. X is a junior), we can therefore expect such usages as That is so junior. And this development will make people feel much more comfortable with examples like the Federer one.