How much of the poor missile success was because of the restrictive ROE?
Lots
Was there even a restrictive ROE?
Very
Or was it more to do with the early missiles developmental immaturity?
Yes, that too.
Once in close, the MiGs were lower wing-loaders than, say, the F4 and new skills were needed to take them on. That's how we ended up with the aggressor sqns.