That's a college try for sure! Two things are working against the annotated short-form of this monster.
First, I think A5E in particular - where that stat block comes from - has a more complex design (compared to 2014 5e) that makes shrinking stat blocks more difficult. Ambusher, Ruthless, and Acid Spite are examples of this increased complexity. I think the design gestalt of A5E works against this kind of extreme condensing.
Second, legendary monsters are always going to be lengthier; even in short-form by at least 4-5 lines.
If we imagine complexity as a dial, with this sort of complex monster we can turn it up to a 3/4 page stat block (iirc that's what the A5E ancient dragons take up) or down to a small paragraph. However at both extremes, there are downsides. Too condensed and there's information / clarity loss. Too lengthy and it's hard to keep track of it all.
Anyhow, I'll take a stab at a short-form / in-line text / AD&D stat style version of this 
A5E Ancient Black Dragon...
View attachment 378377
Ancient Black Dragon. LE Gargantuan;
Senses 22 (blindsight 60 ft, darkvision 120 ft); 
Stealth +9 (advantage in water); 
Lang Common, Draconic; 
AC 22; 
HP 367;
 Spd 40 ft, fly 80 ft, swim 40 ft (amphibious);
 
Saves S +8, 
D +9, 
C +14, 
I +3, 
W +9, 
Ch +11; 
Defenses Acid resistance, Legendary resistance (3/day); 
Multiattack (x1 bite or acid spit, x2 claw) x1 
Bite +15 (15 ft) 4d10+8 piercing and 2d8 acid (grapple if target can’t see dragon), x1 
Acid Spit (60 ft, DC 22 Dex, 4d10 acid and 2d10 ongoing/half), x2 
Claw +15 (10 ft) 3d8+8 slashing;
Special Attacks Acid Breath (re5-6, 90 ft x 10 ft line, DC 22 Dex, 19d8 acid/half), 
Reaction Tail (when creature within 10 ft hits dragon; tail +15 3d8+8 bludgeoning and push 10 ft), 
Ruthless (1/round after critical hit make claw attack);
Spells spell save DC 19
   3/day 
fog cloud, pass without trace, legend lore, speak with dead
   1/day 
create undead, insect plague
Legendary Actions (3) 
• 
Darkness (40 ft sphere magic darkness w/in 120 ft)
• 
Roar (120 ft burst, DC 19 Cha, frightened, repeat save)
• 
Wing Burst (15 ft burst, DC 22 Dex, push 10 ft and prone, then dragon flys 40 feet)
CR 23 (50,000 XP)