I recently replaced my standing rigging and upon tensioning, I realized I am having the same problem as you with my compression post and base. I'd appreciate any photos or additional information you have on the work you have done since I'm now considering the same. I have a Bahama 30 which, I believe has a larger compression post but I don't think Islander solved the problem buy just beefing up the post.
Yes I think that would not solve the problem. After we sawed the sole open this exposed the teak block that the sole sits on. But the sole is a two layer fibreglass structure at that point, with an air space in between that sags over time. After we chizzzzzeled (i don't know how to spell that) out the teak block to see what was going on under there, we found about a pound of hard composite bedding compound made of some sort of resin and fibre mix. The block had a vee in the bottom that was supposed to sit in the vee of the hull and it was kept in place by this compound. But that stuff had crumbled and shifted a bit adding to the problem Once we got the block out of the way, it was an easy matter of making a flat spot in the vee hull with fibreglass, and then making a larger flat bottom teak block to sit on the new flat surface. This block extends up through the sole and the post sits flat on top of that. I admire it all the time. That fellow from Blaine WA did such nice work.
I hope that helps you some. It sounds hard, but it really wasn't.