"It just means you don't spend a boatload upfront on kit."
That is understating it.
One of the huge advantages of public cloud is that you pay for actual utilization vs scaling to peak. That is huge. It would be worth using public cloud just for that benefit. As anyone who has ever sized on prem infrastructure knows, you scale to peak (meaning that you are paying for infrastructure every day as though it is the busiest day in the history of the company, even though most days are not the busiest day in the history of the company) and then you add 20% to the sizing because no one can be certain that the peak will not increase at some point and you cannot just elastically add scale. That equals many, many billions of dollars every year in infrastructure which is purchased and never or very rarely used.