Li Shenron
Legend
Fewer skills and feats are a general result of the 5e system, not of monsters design specifically. In fact it's not true that the dragon doesn't have skills, when in fact everybody in 5e has all skills! The difference is that now you don't need to print out a long list of skill bonuses because you use basic ability checks for everything you're not proficient (only your ability modifier applies). So there's no point to write Perception +2, Insight +2, Survival +2 etc. when basically they are all simply Wisdom +2 checks, and you already have this info in the 6 abilities. There is only a need to list those skills where the creature has a different bonus (normally, those with proficiency).
And feats aren't mandatory for monsters just as they aren't for characters. In 3e feats were mandatory also for monsters, so when describing a monster, the designers had to pick a number of feats depending on the HD, even if it was pointless for the monster concept. Now the designers can give the monsters some feats if they think it's important, but that means we'll see way fewer feats than in 3e for monsters.
These are 2 simple (and neat) reasons why a 5e monster already feels "lighter": less clutter in its description block!
That said, the dragon has lost primarily its spellcasting abilities, for which I said before that I really hope there are rules in the DMG to add class levels or simplified spellcasting to a MM monster (but IIUC dragons in the MM already have some simple spellcasting variants?).
Even tho I am a huge fan of spellcasting dragons, and I feel dragons to be very diminished without spellcasting, you can certainly see from the listed spells that only a few of them were relevant in combat:
Sorcerer Spells Known(6/7/7/5; save DC 13 + spell level): 0—arcane mark, dancing lights, detect magic, ghost sound, mage hand, read magic, resistance; 1st—alarm, divine favor, magic missile, protection from good, shield; 2nd—cat’s grace, darkness, shatter; 3rd—dispel magic, protection from energy.
I underlined those that I would have had the dragons use in combat (a couple of others are "buffs" that I would have cast beforehand, but let's not open that can of worms).
Once again, I am a huge fan of having this sort of spellcasting to some monsters, including apparently useless stuff like arcane mark. The problem is that most people just want to use this dragon in a combat encounter, so the non-combat stuff gets in the way when trying to use the monster's description, because you have to sort out which spells make sense to cast in this round from a long list. Maybe in the ideal case, a monster manual would have had separate sections for combat, interaction etc. but it probably would have required more space, and we know they ran out of it.
