No rule in prior editions either and no rule in 5e and dragons flying?
Was this a 4e thing?
Cus...
i was pretty sure that in 1-2-3e editions (some at least) there were rules that said:
Dragons can fly.
Trolls regenerate until they were finished with fire (do not recall acid frankly.)
So, that covers there were rules for those in prior editions that did not require rules of awesome cool nifty blah blah blah.
Similarly, i am pretty sure that in 5e there are rules for:
Dragons can fly
Trolls regenerate but this is stopped for a start of a turn if they took acid or fire damage and only die if they start at 0 without regen. Also rule for Chill touch to stop the regen too for its duration. Also rules for severed parts/pieces and when they die.
Now these are different a tad from previous editions, establishing their own structure and mechanical results - but yep there are rules for these in 5e... again no rule of cool, nifty, blah blah needed.
Obviously, GM can add rules or change rules etc and put on there "i am so friggin' cool" hats all the times they want as long as they have players that agree... but that doesn't make claims about lacks of rules and lore or rules confusion any more of a thing.