Absolute nostalgia filled BS. 5th edition is my favorite edition, and in fact the edition in which I started playing 40K, but you're peddling BS. The fact that Leafblower lists even hit the meta competitively is proof that your assertion is silly.
I never said it was a perfect edition. there were many rules used in 3rd, 4th, 6th and 7th that should have been in 5th, and are in our current house rules version that we still play. however looking at one gimmick list among the many that existed in each edition (iron warrior oblit/defiler spam in 3rd/unkillable eldar tank armies in 4th, lash prince armies etc...however players could find a way to break the game) doesn't change the fact the overall mechanics of 5th are still better than the way 8th has turned out.
One sided battles still did happen but not the the extent and speed that they do currently. most often it was a game where you were either hoping you got or didn't get that extra random turn past 5 since it changed the outcome of the game drastically. An example of that was a good friends super powerful eldar corsair list with hornets, warp hunters, some of the fighters, dire avengers and occasionally wraithguard. many times i fought him to a draw(often to my suprise) even though his army was chock full of S8 AP2 weapons and eldar shinanigans
I don't know how much you played of each edition but i played alot more than some. in 3rd and part of 4th i was single and was at the game store fridays and saturdays (and sometimes slept in my car to game from one day to the next for more game time) as of 2008 i became a store volunteer employee. i now limit my time to one day a week but it is usually 12+ hours for that day.
Up until 6th ed dropped 40K
was literally the core of my gaming hobby aside from battletech. in that span i had full armies for -dark angels standard, ravenwing, deathwing, sisters, nids, tau and salamanders. i do not consider it nostalgia at all since i am still active with 5th ed. but rather a long catalog of continued experience and comparison with other editions.
8th is for lack of a better explanation an entirely different game to play than everything previous(like the switch from 2nd to 3rd). with some good ideas but overall a terrible edition by comparison given things like the subject of this discussion where you can have a TT
tactical wargame that now depends more on list building combos like a magic deck than it does on what actions you take on the TT
where games end up being decided in 2 turns and certain army types like melee oriented lists do not function effectively.
On the up side at least it isn't as bad as 6th, even GW
figured that out and killed that edition after about a year.