Funny, this just came up in a book I'm reading. While the use of healing kits in D&D 5e are certainly incredible, it is in keeping with the genre.
I am reading The Swords of Lankmar (Fafhrd and the Gray Mouser Book 5), part of series of books that was incredibly influential on D&D, and I just read this passage on my lunch break:
"In two heartbeats he [the Grey Mouser, a Rogue/Thief] had turned his back on his assailents, darted past a somewhat startled-looking Frix and Hisvet, and burst out through the branchy wall of the closet-bower amidst a second and even larger explosion of white blooms.
"Five heartbeats more and as he scurried north across the Plaza of Dark Delights in the light of the new-risen moon, he had buckled on his belt and withdrawn from a small pouch pendant on it a bandage which he began deftly to wrap tightly about his wound.
"Five more heartbeats and he was hastening through a narrow cobbled alleyway that led in the direction of the Marsh Gate."
Considering that a well-trained athlete has a
resting heartbeat of about 40 per minutes, we are talking about 7.5 seconds, at most. Given that he just killed to Mingol assasins and was making a hasty retreat, it would have been under 6 seconds (7 heart beats). Actually, all 12 hearbeats probably took place in under 6 seconds given the rate is heart would be beating under the circumstances. Yes, I'm taking "heartbeat" too literally but don't think it is stretching the workds to far to conclude that:
In ONE ROUND the Grey Mouser disengaged, took full movement, and applied a healing kit on himself. Actually, he may have even "dashed" and still was able to disengage and apply a bandage.
The D&D 5e rules are certainly in keeping with their inspiration. If anything, they are too conservative.