Contrary to some, I actually like how difficult it is to design perfectly challenging encounters. I find it more thrilling when some encounters are easier than expected and others are harder than expected. For over 30 years, I've been running games and designing encounters not so much based on predetermined challenge levels, but more on story appropriateness. Random rolls that change the tone/direction of an encounter can be very exciting. Using the CR and xp budget as a guideline doesn't have to be exacting for my gaming experiences.
I've also experienced my fair share of deadly encounters as a DM and player over the past few years (although most of our experiences have been from level 1-8). Death is very real in 5e. The death saves are definitely tension building especially when a player rolls a "1" or the foes deal damage to unconscious PCs. If a DM uses the death save as a threat, the players play their PCs much more carefully.
Party size and number of foes is really the number 1 determinant of encounter difficulty with 5e, and to me that makes perfect sense. Small party will have more swinginess in combat. Larger parties will be much more competent if combat is the chief obstacle. Not that D&D has to emulate real world, but this is completely intuitive based on real world experience.
For my own preferences, and excitement in combat, I prefer playing with 3-4 players rather than 5 or more.