So is the base console holding back the mid gen if that is still the target?
If, do you mean, it will hold it back because games will not be made to target the Pro fully (in such a way that the game could be made for the base console), then yes, the base console does hold it back to a degree, but that's not the point of 'mid gen' consoles. Most people buying mid gen consoles already have the base console and want extra performance, whether thats 60fps over 30fps, or higher resolutions. This is because they are ready for that extra power after having owned the base console for a few years. Its understood (mostly) that the Pro version of these console will never fully be utilised (at least have features that could never run on the base console, well, unless those can be cut without affecting the base game, you could not have a physics based game when the physics don't run on the base console for example)
This is mid gen, not a new gen.