I dunno...... Ebby Thatcher was Bill's sponsor and Ebby kept going back out DRINKING. On the other hand, Bill had a huge support group of preachers, priests, therapists, psychiatrists, and fellow AA members.
I think, sometimes, we put too much emphasis on our sponsor and expect, hope that they'll be all things to each of us.
I'm not so sure about letting a good sponsor go just because I need work that they're not able to do. Do some net searching for Steel on Steel. Mark Houston out of Texas started it in AA for just this reason......because he felt it was selfish to continue to expect his sponsor to sacrifice time with newcomers to spend it with him going over stuff he "knew better" than to be doing anyway.
I've gone to some of the folks I really respect in the groups I frequent and given some of them "spiritual license" (also a concept I got from Mark H...... check his talks out on XA) so they can feel free to call me on ANY of my BS anytime they see it......and I don't get to argue back. They know I have a sponsor.....but they know I want more help.......so they're like assistant-sponsors.
Just another something to think about and maybe try.
That said......sometimes it's just time to go. And if that's what time it is.....well.....your sobriety has to come before a great friendship with a sponsor. That sux but getting loaded or backsliding in your sobriety sucks worse.