To give you an idea of what “bug free” means, all bugs in this thread List of unfixed bugs - #96 by GMEvangelos should be fixed, which they fail to do for months (some exist since launch). I’m not even counting the countless bugs that only grow day after day on the Report a Bug forum.
They could spend a year doing nothing but fixing bugs.
No game is perfect. But the bugs of aoe2 de receive way less attention than they should receive.