Having AWS, Azure, or GCP validate your technology, product, and market is a huge win. Being the prime creator of the product puts you in a very advantageous position (new features, deep support, better user experience). Like the “normal” open source channel, you don’t collect all of the funnel. You do get a new channel (users of rival cloud providers) that operates at a disadvantage compared to your offering (at all but scale, and that’s not an impenetrable one). Those are well qualified users, accustomed to paying for the software. They’re great leads.
Downstream competitors are net good for you. Yes, it means other people get some of the revenue. But some of those would never have used the software in the first place without that competitor, or wouldn’t be used to paying for it. The increase in usage more than makes up for it.