How does the workspace work?

Hi all,

I know the subject is really vague but please hear me out.

I know that one power bi workspace can have about 1000 reports. I also understand that reports in import mode are much faster than the other two options. Assuming we have about 300 reports with different data sources in different modes (live or import etc) and about 100 active users using them at about the same time. I have heard from the users the reports are slow. We have tested individual reports and they seem to be working fine. but when the above scenario occurs it is slow for everyone. 

My question is how does the workspace handle multiple reports with multiple active users accessing it at the same time? I m just trying to get my head around it.

(Note: Yes, I know the reports need to be optimized and all that. Assume everything is optimized already.)