Yet that is my problem with it, as a DM I don't want to waste all that time at the table.
Which stands in frank contradiction to the fact you just outlined the mechanics you use to solve it! Shared rules are there in part to proactively resolve issues that all DMs are likely to encounter in their games; or to put that another way, to communicate resilient solutions to those problems to everyone. While I would agree that we don't know the ideal solution to this issue today, we do know a number of mitigating rules for play and WotC's design efforts should buttress rather than undermine those rules.
I wouldn't consider an adventure's random encounter elements to be part of the game's rules since those random encounter elements only apply to this single adventure. In another adventure, I could easily design the adventure differently so that planned encounters domino into each other, creating a string of encounters that still satisfies the 6-8/day paradigm.
I look at it like this. In order to satisfy the OP's needs, we'd have to rewrite the entire game. The entire Monster Manual would need to be rewritten in order to make individual monsters more of a threat so as to satisfy his need for single encounter days. Additionally, classes would need to be rewritten so that every class balances over the course of individual encounters, instead of over the course of a day.
IOW, we'd need to rewrite 5e to use 3e style monsters and 4e style character balance. While I understand the impetus, I'm also very realistic in that this is just not going to happen. There is no way that WotC is going to do this. It's a pipe dream.
So, being the pragmatic person that I am, I offer solutions that don't require rewriting the entire game. Plan your adventures such that you are no longer relying on single encounters to provide an adequate challenge. We did this in 1e all the time since 1e monsters individually compared to the PC's were extremely weak. So, you designed adventures where you had waves of baddies, strung together encounters, and a much more restricted recovery rate.
IOW, the solution to the "Elephant in the Room" is to either accept the system as it is and work within that system or find a different system. And, AFAIC, that's the long and the short of it.