Well, I'm following @Imaro in talking about the game as presented.How different does it have to be to not be D&D anymore by yours and @Imaro 's judgement? How much homebrew is too much homebrew to be allowed to be called "actual" D&D in this discussion?
Hit points - as level-relative skill, luck, puissance, divine grace etc - have been a core mechanic from the outset. Likewise saving throws.
Disease has always been peripheral in comparison; and the rules didn't even touch on thirst and starvation for around their first decade of publication.
As you've often seen me post, RPGs like RM and RQ are direct reactions to the core mechanics of D&D. Asserting that D&D would be more like itself if it was in fact more like these other RPGs that reacted against it seems silly to me.
As to whether it is worth trying to drift D&D in that more simulationist direction - I did a lot of that work in the late 80s, building on proficiency systems found in published AD&D books and fan systems in magazines. I wrote up spell lists (fire spells, enchantment spells, travel spells, etc) and worked out a proficiency-based approach to spell list specialisation. As soon as I was introduced to Rolemaster I dropped all the work I'd done - someone had already done it, and it seemed more sensible and straightforward to take the benefit of their work.