This.All the issues I've ever encountered as a DM or a player have to do with the encounters with dragons.
When you are ready and geared up for a battle with a dragon it can be easy as pie. When a dragon falls out of the sky and burns everything in sight then it can be deadly.
Until dragons get good at spellcasting, they can make for tough but not inappropriate encounters for their CR. Their most dangerous tool is their breath weapon. If that is neutered because the party has protection against it, a dragon encounter can turn into a yawnfest.
In my game dragons had another important tool: reputation. Until the party reached high levels they never really dared to fight a dragon. They were much more likely to surrender or try to bargain.
As has been mentioned, dragon encounters aren't meant to be routine. If the dragon's purpose is to be fought (and slain), the DM will have provided opportunities to gain advantages against the dragon, even if it's 'just' information.