Then in all honesty, I do not think you have ever seen an MJ Axanthic.
I live 20 minutes from Mark Mandic(the originator of MJ Axanthics and, have seen his snakes on several occasions and have yet to see any or any that others have purchased from him brown out), I've asked him specifically about this issue.
Granted they are less common so there are fewer examples to compare but, even when not mixed with "cleaner" genes all that I have seen have held colour very well.
And, I will say I have seen some very nice TSK line snakes but, I have seen more nice VPI's. And, I've seen some pretty bad examples of both. I believe (but this is just a hypothesis not anything proven in any manner) that attention to detail may have been responsible for the good examples in both lines.
Must be a different line of "MJ" Axanthic. I was under the impression Mike Jolliff was the founder of the MJ line, which I have seen many many times. It could be that we are indeed talking about different lines.