Is Power BI report server naturally slow?

First, analyse ExecutionLog3 to check what is slow, if model processing, open report definion, model loading to memory, or dax queries. Second, check you server resources, especially memory a CPU utilisation. Also check how often are report wipe-out from memory.

For comparsion, in my enviroment, I must install second PBIRS server in scale-out mode, and dedicate background model processing to second server (and first server only as PBIRS front-end). My experience, model processing, and also dax query performance is fully comparable to cloud Power BI Service. But report open (authentificate and definition load) and load model into memory (if not already loaded), is little slow (but not big difference}