With no interdiction ships can just infinitely FTL away from incoming attacks making combat in space completely ineffective.
That doesn't account for change times. Space combat is going to be near some planetary (FTL-hindering) body the vast majority of the time anyway.
if you're going to remove interdiction you need to put in something else to prevent FTL use.
No we don't. Also, there's still the graviton beam hold method.
Or to put it another way, How does this promote RP at all?
It keeps plot ships and other ships from being rendered immobile and unable to escape in open space, forcing the space battles of the SARP to mostly occur around known landmarks such as planets.