I think it depends, honestly. As a startup you could be using civo or katapult as clouds and be getting almost everything you need. I think the main issue is actually network effect; easy to hire people who know AWS, easy to explain AWS architecture to a auditor who's seen it 100x before and it's easy to explain to customers that you use AWS like them, so easy to do VPC peering, or BYOC with them if needed..

If you just want dedicated servers/VPS the choice is much wider still and plenty of providers on comparison sites and so on.