It is a startup, not a space program. Backup can be done with simple ssh+rsync script. Patching is a weekly weekend cron script+reboot. Some heartbeat monitoring... If it goes down for a few hours, not a biggie.
For "throw it all in a PaaS" you need dedicated person, monitoring, billing etc... It is more expensive, not simpler. Cloud provider may also terminate your accounts, change settings etc...
If I had a nickel for every time that restores from "simple SSH+rysnc script" backups failed, I would not need my job as an infra engineer. You can do that, but being sure they work is hard
My clients spend a lot more on AWS bills than they would on self-hosted infra; $1000ish compared to $200/mo from self-hosted or a pair of $1000 servers colo'd for about $100/mo. They get a lot more - Reliability and support channels. That's what they're paying for. Absolutely, I recommend that they when they scale, they move their most expensive parts in terms of AWS costs (bandwidth-intensive things like gameservers and media bouncers) from AWS to self-hosted, because those are the things that are too expensive on AWS and have reliability properties where "Throw a bunch at the wall, fail them fast" is a good guarantee. For your production backups, don't rely on simple scripts. Don't rely on complex scripts. Rely on commonly tested solutions of other people's amortized experience.
SSH+Rsync is the wrong way to go about it, you will fail to restore backups. You need something that allows you to make snapshots. Fortunately that's easy and cheap if you use something like Proxmox.
For "throw it all in a PaaS" you need dedicated person, monitoring, billing etc... It is more expensive, not simpler. Cloud provider may also terminate your accounts, change settings etc...