Even though I agree with you, I think I might support slightly different definitions of rape as I think it could help conviction rates and that is the biggest problem - each time the jury are effectively having to re-define rape whilst the defence lawyer points out things the defendant didn't do (no violence, for example). I know it has been defined and should be simple, but it isn't proving to be.
It isn't saying it is more serious in one form, any more than saying GBH is more serious if you lose an eye than a hand, but it would make things very clear for juries. There is a premeditated part to some rapes (breaking in, spiking drink), which doesn't change how it affects the victim, but might make the person more likely to rape again and, like murder, that should be reflected. Such definitions would help profilers and research and any such information is useful when we are looking at such low conviction rates.
If there was a category of "domestic rape" say, where someone rapes their partner, it would help convict the rapist if this was not at all open to debate as a crime, and if they could show evidence of other misogynistic behaviour that fitted the profile of a domestic rapist. No comment on relative serious-ness compared to other crimes but a way to gain more evidence than one word against another.