That's a snappy take, but it definitely doesn't feel that way to me as someone who did use mainframes a bit and big shared unix servers(not mainframes) quite a

That's a snappy take, but it definitely doesn't feel that way to me as someone who did use mainframes a bit and big shared unix servers(not mainframes) quite a lot at points in my career. The defining characteristic of the mainframe experience for me is extreme rigidity. Upgrades are practically impossible, scheduling time on the mainframe requires lots of forward planning, notice or having a close relationship with a sysop that you can buy drinks for to get jobs to jump the queue. Cloud on the other hand brings scaling on demand scale up/scale down for bursty workloads, very quick to experiment with different configurations etc. The exact opposite - flexibility is very much the name of the game. Shared unix servers (not mainframes) were also very different from cloud in this way but also had the difference that you were always in very noticeable contention for CPU and io with other users, whereas on cloud you are almost always on dedicated resources for your use case. I never really felt contention on mainframe workloads because they are so goddamn slow all the time it's pretty much impossible to tell if you're contended or not.