It's easier to massively over provision or use the cloud than it is to get good at capacity planning. Same as how it's easier to use a GC than it is to do manual memory management.
They are all valid strategies, the key is picking the one that suits your situation.
If you need a small to medium amount of resources then the cloud is likely the cheapest option.
If you need a medium to high amount of resources then massively over provisioning can still be cheaper than using the cloud.
The cheapest option for anything medium size and above is physical servers with good capacity management.
Good capacity management requires good internal communication between business units. And making predictions based on expected/planned events not just historical data.
They are all valid strategies, the key is picking the one that suits your situation.
If you need a small to medium amount of resources then the cloud is likely the cheapest option.
If you need a medium to high amount of resources then massively over provisioning can still be cheaper than using the cloud.
The cheapest option for anything medium size and above is physical servers with good capacity management.
Good capacity management requires good internal communication between business units. And making predictions based on expected/planned events not just historical data.