Is saving 50% also a worthwhile goal at expense of being on prem, and all the downsides? Asking honestly because that’s where my business is in terms of the decision. We won’t save 90% but we will save 45-55%.
Remember that the choice isn't simply between AWS and racking your own gear. You can make big savings by just renting Linux servers from hetzner or similar. They install and repair the HW, you get ssh access just like with a cloud VM. You just have to make sure to monitor it so if there's a failure you can file a ticket to get components swapped out.
There are a lot of variables, but unless the 50% savings isn't much more than enough to hire a very good ops team, then no, I can't imagine that is enough savings to make the trade-off worth it.
Is your company experiencing rocketship growth or are you at the point where your growth has stabilized to a modest figure? It's probably best to pursue growth over cost savings, if possible. But not every company is in a position where a few more features can double revenue.
Still, I think it's hard to justify going anti-cloud in an effort to cut costs. Without a very skilled and experienced team doing the migration, the end result is very likely to be some hybrid setup that's the worst of both worlds. Especially if you're using a managed service, the open source alternatives might not be the drop in replacement that they claim to be.
Is your spend 2% of revenue? 5%? 50%? Saving 50% of 2% is almost certainly not worth the risk. The bigger your the percent and your revenue the more likely you should do it. Dropbox again is a good example.