Reduce the stat block. It's wildly oversized. Remove most of the numbers and stats listed. Use that space to include some of the text from older editions that helped with making the monsters more interesting. Like adventure hooks, common goals, tactics, monster roles, lore DCs, number appearing, encounter groups, ecology, etc.
Something like this would more than suffice as the actual statblock.
Gnoll. AC 15. HD 5, hp 22. Attack +4, one per round (bite, spear, or bow). Damage 1d6+2. Move 30 ft. Checks +2/+0/-2. Morale 8.
Rampage. Reduce target to 0 hp, bonus action to move 15 ft and bite.
There's nothing in the full statblock that's necessary to run a gnoll that's not also represented in those two lines. Stats are all +2 to -2, that's the "checks" entry. Pick two stats for each. Should be obvious from the monster. CR is a terrible design. We don't need to waste space on it. Everything has darkvision, especially the monsters. It's not a question of if, rather how far. Almost always 60 ft, 120 ft, or 360 ft. Pick one. Passive perception? It's either 12, 10, or 8. Pick one. Ranges break down to melee, short range, long range. Almost nothing happens at long range in D&D. Listing ranges for the same weapons for every monster in the book is a waste of ink and space. Averaged the damage across the attack types. They're only descriptive differences.
This eliminates redundant information and saves a heap of space...so we can have all the goodies back from older editions I mentioned above.
It is abundantly clear that many of the designs of the various monsters were never actually playtested, or frankly, not sure they were designed by people who actually play D&D. I have to fix most stat blocks for actual game play.
While I think your simplification goes way too far, there is no doubt that some monsters could be simplified, and oh so many fixed. Most are vastly underpowered. I posted in a previous thread about the CR 8 Deathlock Mastermind in the real Mord's. The statblock, among other things, has:
Stats for this creatures skills (of course only 3, instead of the minimum of 4 that any Warlock would have)
A 17 on Cha, which given this is a 10th level caster, would have a minimum of 18 by that level.
A +1 to Wisdom saves (no Prof in Wis), but does have Prof in Intelligence. Remember, this is built from a Warlock.
Blowing an Invocation for this monster to be able to Detect Magic at will.
So imagine this scenario.
A group of woefully undergunned 5th level chars enter the lair of this CR 8 BBEG. One happens to be a Cleric. That char, upon seeing the BBEG, uses the Turn Undead feature. At 5th level, a Cleric has a minimum of 18 Wis. That makes the DC for the BBEG to meet/beat DC 15. The Deathlock gains Advantage on said save, but even with Advantage, the chances are 42.25% this 5th level Cleric effectively ends the encounter with a CR 8.
WOTC, well at least its consumer base, would have been better served hiring competent designers and play-testers to actually correct the statblocks, rather than introducing new playable species and dumbing down the bulk of the monsters in that new book. Oh, and if anyone things I am being too harsh on WOTC, Todd Kenreck posted on Twitter yesterday about how Nat 20's actually matter in D&D skill checks. When people at his level in the company do not even know base mechanics......
