You misunderstand. 6-8 encounters every day shifts the game into directions that are problematic to story & setting... Pointing out how someone died in your game to a save or die effect underscores rather than contradicts my point though since I've been saying those effects are the only thing that poke the fear buttons on the player's lizardbrains. Just like when I mentioned playing games & sports with a toddler, I can do things to make it interesting & adjust the difficulty but I have many more options to functionally do so than MMA reenactments like disintegrate or accidentally/intentionally tripping him to drop hp to 0 then just stomp the body a few times (knock out, first first two death saves with a repeated attack, do it again). People are not ragging on 5e because it's hard to kill a PC, that's happening because you need to use save or die monsters or homebrew & houserule in the ability to ever scare or give pause to a player unless you run a murderhobo zerghunt. Things are not helped by the fact that an overly streamlined system means lateral advancements that don't change a PC's power level are mostly off the table
I have no problem getting between 5-10 encounters between long rests, and no the group are not murder hobos. For my style of game I use the alternate long rest rules*, but the last couple of sessions I've had to go out of my way to even give them a short rest (overnight).
I also have adventure days regularly span a couple of sessions. As far as putting the fear of god into them, I don't think it's always necessary to have the players on the brink of a TPK. Having it happen every once in a while is a lot more fun.
In my last session (random encounter during a short rest) a wraith popped in, critted and nearly turned the PC into a fellow wraith with one hit. She spent the rest of the session with single digit HP since there was a deadline and they had to press on. It was actually a pretty brutal session, I had multiple encounters with PCs on the ropes no custom monsters or house rules in sight for this one.
So if 5E isn't challenging enough, maybe it's not the fault of the rules. At least it isn't for my group.
*I could easily tweak the timelines to follow standard rest rules, but I run a very investigation/RP heavy game so longer rests work better from a story POV.