In lairs, dragons should have minions and traps and other tricks. That isn't cheating, it is just playing smart. But also, dragons should maximize the utility of their movement. No self respecting dragon is going to fight in its lair for long. At worst, they will do loops until their breath recharges so they can hit the party hard.
I get the feeling some folks feel "bad" if dragons play smart. Don't. That's what they are there for. You don't live centuries or millenia without being smart.
PCs should either plan, or run. Do not give them an easy out. Dragons are the pinnacle of BBEG play. Make the PCs work for it, and kill some of them.