> How hard is it to create a competitor to infura?
Infura is merely hosting nodes for you and exposing their JSON RPC endpoints. They did not _create_ the API.
There's already plenty of competitors in that space. QuickNode and GetBlock for instance, if you want mutualised/managed nodes. You can also host your own node yourself, or use e.g. AWS Blockchain to host it for you, or even use the public free hosted nodes that most blockchain project provide. It's just a Metter of trade-off between cost, time and security.
If you are using JSON RPC APIs (which most people do) there is nothing that locks you to Infura or any other provider.