I have lots of good things to say about your basic premise, but I wanted to break out one thing first.
D&D 5e is 'easy mode' because of the DMs, not the rules. We can put in place rule fixes so that DMs mess up less, but it in no way 'defaults' to easy mode, it's just run that way.
If played by designer expectations it's fine. Designer expectations include (but aren't limited to):
- 6-7 encounters per day, with 2 short rests about 1/3 and 2/3 of the way through (2014!DMG, but since the math hasn't changed much this still stands). And remember, 6-7 average encounters means that day you only run 3, also run a day of 10.
- Standard array or point buy. Rolling both can give higher starting numbers which means feats sooner, and "somehow" seems to average a lot higher than statistics says it should unless the DM witnesses all rolls.
- 5e expected amount of magic item. They took item math out of character advancement, but many DMs are still calibrated to earlier edition amounts of treasure. It's much lower then expected. There's a chart in Xanathar's on pg 135 that breaks it down for the whole party, yet many DMs give out more than that per character. BTW, if you strictly rolled on the 2014!DMG charts (and had no magic items shops) it would average out to these numbers, that's where they got them.
- Round-up-Average HPs (max at 1st)
- No house rules giving more, like a 1st level feat. Something I was just told was the #2 most common house rule in some parts.
Play with these, which are all in the rules, and you'll match what the designer expectations, and find that it's not defaulting to easy mode but a more reasonable difficulty.
I've jumped out of 5e for a bit, about to run 13th Age 2nd ed, but my next planned 5e game I was going to use something akin to the Gritty Realism variant of the 2014 DMG, where overnight is a short rest and between adventures/sanctuary like Elrond's is a long rest. Between that and me being conscious of the rest I can meet those expectations.
The problem isn't the mechanics per se, it's that designer expectations and how people actually run differ a lot. They don't even follow these well in their adventures. So it is a mechanically fixable problem, but saying the D&D 5e is easy mode is just an incorrect statement -- played as expected it is not.