I did the same thing by removing those 8-12" LMB when I started managing my pond but I wasn't seeing a big improvement.
I did start noticing the RW of those 8-12" bass started improving but not the larger bass.

I've heard Bob talk about it and others that once a bass is stunted that is weight that he can't make up. When I started tagging my bass I started seeing larger bass that I recaptured with very little weight gain, some maybe growing only .5" and 5 or 6 oz. in a two year period.. That's when I started adding larger 14-16" fish to my culls and then I started seeing those RWs for those size fish start to improve.

There were other variables involved for sure but I believe those larger fish were stunted and not going to reach their potential. I believe that gave the 8-12" fish that I did not cull a chance to continue to grow once they reached the 14" range and they did not lose that growing season... therefore they had a much better chance of reaching their full potential.