AWS is not cheap because of your server costs.
AWS is cheap because of elasticity, velocity (opportunity cost of next feature), and reduced maintenance hours.
"The cloud" was never (afaik) was about getting a cheaper VPS. It was about being able to get them on demand, give them back on demand, and generally not have to maintain anything besides your code (and maybe apply updates to datastores / AMIs)
Now, if those premises are not true for your startup/business, then AWS is not the tool for you. I didnt see any analysis of ongoing maintenance costs in the 800k saved, but will it take 1-2 FTE engineers to now be more oncall, more server upgrades, more security patches etc? That's easily 1/2 that savings gone already.
Edit: for the most part these attributes apply to GCP, Azure, Heroku etc as well, its not just about AWS