Whilst the default aircraft are not bad for AI, most addons are! they destroy your framerates and bring the game to a standstill as they are often computer resource heavy.
There are aircraft designed especially for AI and not for user flying. They are designed to have a minimum impact on framerates. Also, they have flight dynamics designed for AI - flyable aircraft often don't perform well as AI
If you want AI airliners the best place to start is at
Project AI
Click on "Official Files"
Download the PAI installer - and the FAQ
Then download some airline packages and instal them.
You will probably find that you won't see as many aircraft as expected - that's because the default airports don't have many parking spaces. You will need to increase the parking spaces at places like EGLL, KLAX, LFPG etc etc.
In that case you need a tool called AFCAD. A good place to start is
Project AI AFCAD