The downside is you are walking into an inviting mono/duopoly.
Things like this and cloudflare are amazing until the wind changes and the entire internet has a failure mode
In my experience, the biggest risk with AWS and similar is not the dependence itself, it's the cost. With AWS you pay a lot more for the compute then if you just rent the hardware for $25/server with Linux, and then go from there. It does make sense for some shops, where you have scale and can make calculated trade-offs between 100s of engineers' salaries and cloud costs (like Netflix).
But I think a lot of small startups end up overpaying for their cloud costs even though they don't take advantage of the elasticity/scaling/replication/etc.
Also, a lot of BigCos are just on public clouds because that's the thing now, but their stacks, software and teams are so broken, they don't actually take advantage of the cloud. Their engineering teams are mediocre, and so is the software, so it breaks all the time. So they end up paying for something they can't take advantage of, because they don't need to scale, they don't need high uptime and/or can't achieve it because their stuff running on top of the cloud is a horrible unreliable spaghetti anyway.
If I was to do a SaaS-y startup today, I'd just rent cheap dedicated hardware, I'd use OVH [1]. I'd start with 1 reasonably beefy server for like $25-50/mo and see how far it gets me. I would use S3 for unlimited, reliable storage, (maybe even RDS for DB), but everything else I'd keep out of AWS, running on my cheap server. Ie. I'd keep my data in AWS, because that's super cheap and worth it.
Later, if the thing is super successful, I'd go to $250-500/mo and get 5-10 reasonably beefy servers, and start to move things apart. I'd still not worry too much about replication and such, I'd just to backups, and take the hit if there's a problem and restore at the last backup point. I think this would get me pretty far, all the way to when I want to bring BigCo customers aboard who need all sorts of ISO standards and such. At that point the whole thing will stop being fun anyway and it's time to let other people worry about it..
And in terms of hiring, I'd make it clear at interview time that this is the stack, and we're not going to do microservices and Kubernetes and all that crap just because others are doing it, and I'd hire from the remaining pool.
[1] I've been on it for my personal devboxes for ~7 years, it just works
But I think a lot of small startups end up overpaying for their cloud costs even though they don't take advantage of the elasticity/scaling/replication/etc.
Also, a lot of BigCos are just on public clouds because that's the thing now, but their stacks, software and teams are so broken, they don't actually take advantage of the cloud. Their engineering teams are mediocre, and so is the software, so it breaks all the time. So they end up paying for something they can't take advantage of, because they don't need to scale, they don't need high uptime and/or can't achieve it because their stuff running on top of the cloud is a horrible unreliable spaghetti anyway.
If I was to do a SaaS-y startup today, I'd just rent cheap dedicated hardware, I'd use OVH [1]. I'd start with 1 reasonably beefy server for like $25-50/mo and see how far it gets me. I would use S3 for unlimited, reliable storage, (maybe even RDS for DB), but everything else I'd keep out of AWS, running on my cheap server. Ie. I'd keep my data in AWS, because that's super cheap and worth it.
Later, if the thing is super successful, I'd go to $250-500/mo and get 5-10 reasonably beefy servers, and start to move things apart. I'd still not worry too much about replication and such, I'd just to backups, and take the hit if there's a problem and restore at the last backup point. I think this would get me pretty far, all the way to when I want to bring BigCo customers aboard who need all sorts of ISO standards and such. At that point the whole thing will stop being fun anyway and it's time to let other people worry about it..
And in terms of hiring, I'd make it clear at interview time that this is the stack, and we're not going to do microservices and Kubernetes and all that crap just because others are doing it, and I'd hire from the remaining pool.
[1] I've been on it for my personal devboxes for ~7 years, it just works