Don't blame Plus-X. It's a nice film.(posted 8366 days ago)ID-11 and packaged D-76 aren't identical; you need to make some adjustment by experiment depending on the film and the dilution. The exact formula of packaged D-76 is not known although many speculations are around. Don't believe them.
It is true that Plus-X does not give the same resolving power as TMX. However, the difference is well within the factor of 2. If you have larger difference, there is something wrong. In my experience PX loses apparent sharpness in highlight especially when overdeveloped. If your neg is too dense, cut back development a bit. Also, PX can't take high temperature when wet compared to TMX which can be processed at a quite high temperature. Stick with standard 20C to 25C processing precisely, including final wash. I don't think it is the factor affecting your resolution though.
Although I don't use it regularly, I personally think Plus-X is the best product EKC has ever made and I like it a lot. If they make it on a modern thicker base I'll buy 100 rolls right away.