Also it's going to be simpler to provision your base (commited use) on the cloud and then handle bursts on the cloud, than it is to have your base on prem and burst to the cloud.
You can buy physical servers in leasing ,turning it into opex
You can also rent them for little bit extra via managed dedicated servers from vendors like OVH.
Not going with a big cloud provider def doesn’t mean that you need to buy physical servers and build an on-prem data center.
...while forgetting to have sane on-call rotation for cloud you also need at least 3 people on that rotation that are also clued in on cloud operation enough. Sure they can be "developers" but if your app architecture requires so little maintenance and flea removal that they are not doing ops jobs much, chances are so would it in either rented or dedicated server env.