I worked for a MSP for many years, and was well acquainted with our regional competitors. Our uptime and theirs was nowhere near AWS-level.

You're getting a different engineer every time you pick up the phone. They most certainly do not know your systems like an internal team would. I regularly saw cascading/circular issues caused by lack of familiarity and/or poor change management.

Owning and administering your own iron makes sense at a certain scale, but it's a much bigger scale than most companies will reach.