That depends on whether those big competitors are contributing code back.
If they are, then great, the code continues to exist as high quality open source, even if you're playing a smaller role.
If they aren't, then the good version isn't open source. Your goal is failing even when you ignore profit. And at that point maybe an "open source except for those guys" license gets you closer to your goal in practice.
Or more fundamentally, don't open source your value prop. Open source your complement. So many OSS shops build a valuable core only to realise their actual business ends up being selling managed servers.
It's not hard to create a profitable business on open source and make good money. The question is how much.
If your goal as a founder is to be a billionaire, open source products are not going to do it. You need monopoly-level rents to do that, like Oracle or Snowflake. There's plenty of opportunity to create millionaires. But you'll have to forego VC financing to do it because that math does not work for venture capital funds.
Sure they do. As the original authors of the product, they should have the best understanding of its features, and are in the best position to augment it in ways other pure hosting competitors can't or won't. They have first-mover advantage to build novel features, and integrate them into commercial propositions that benefit their customers first. They should also know best how to deploy and scale the product, even if their competitors excel at this.
If Redis Labs wasn't able to compete with AWS and other pure hosting providers, then they failed at taking advantage of their position. This is not an indication that the open core model can't be successful for both OSS users and the business. E.g. see Grafana.
Of course, this also depends on the nature of the product. A general purpose database or another core infrastructure product is much more attractive for hosting competitors than a purpose-built product.
If your goal is profit, don't open source your core product.
We've seen this time and time again where a company releases their core software under a permissive license, and then bigger competitors come along and resell a solution redistributing their software.
If the company's central goal is profit, this is an existential threat. However if your company goal is to ensure the software exists (as a non-profit steward), this is a resounding success!
This doesn't apply to software that's secondary to your core product, e.g. a useful tool you've developed but don't make money directly selling to others.