"This will clearly dismiss a nice range of chords. A leading tone only wants to do one thing (naturally) and that's move up a half-step but it doesn't have to. Example: viio - III7(V7) - vi(i). A deceptive move from major to harmonic minor a step and half lower. I get what your saying but don’t you think by shortening the range of chords into either I or V your limiting your possibilities?? Actually any chord is a shape of it’s tonic chord (I or i). So what help is it to think of every chord as a tonic if your a theorist?"

Don't get this at all.
Dims can move by half step and don't have to. Exactly. Understanding, the a dim is a rewritten dominant makes this possible. This does NOT shorten the range or chords, but makes them vastly larger. The real problem is misanalyizing or mislabeling, especially in terms of function. A tritone, in a traditional sense and even transferred to all forms of modern music, is a Dominant Function. May not be at the V7 position, but most always a 5th relative. V7 of something...
This kind of analysis on the street, is almost nonexistant.
Just alter the major scale structure. Most all good session people know this information.

"So what help is it to think of every chord as a tonic if your a theorist?"
I have no idea what this means. I've never said this.
What I did say, that certain chords, most of the time, have a tendency to be a function of I, or V. Again doesn't lessen or shorten anything. Actually enhances. The more the merrier. There has been some discussion of stacking chords on this site. (no talk of stacking scales, modes, quartal harmony, etc.) This idea is very modern an should be understood. It's real simple if you know and understand certain principles.