To add: Dragons generally have Legendary Actions, which are 2-3 actions they can take between PC turns. This helps with action economy, enabling 4-6 PCs vs a single dragon to be a somewhat fair fight. This is different than adding 2-3 actions to the dragon's turn, as that would easily enable the dragon to TPK the party (or instakill a PC) during a single of its turns. Spreading out the dragon's actions gives the PCs a chance to react, heal, reposition, etc.
It will be interesting to see how Larian adapts these Legendary Actions. They're not exactly the same as reactions but are in the same ballpark. If Larian changes dragons to have their normal 3 attacks (or breath weapon) + the LAs all on the same turn, then yeah they're going to have to adjust a lot of details to make balanced fights.
Also, default 5e dragons don't have spellcasting (there is a MM variant where they do). So it'll be interesting to see if Larian gives them spells.
Also also, dragons have a decently high flying speed. I assume that Larian will change this into a jump/pseudo-fly, probably with a simultaneous disengage. Maybe with the Wing Attack (which has a knockdown effect) upon landing?
