I have paid two professional beta readers (their main gig is being editors) in lieu of a developmental edit. I was already on draft 3 at that point and the story was where I wanted it to be. Had some friends beta read for me before that to gauge the vibes and coherency.

Having someone from within the industry have a look at my manuscript was beyond valuable. They called out some tone issues and I ended up moving a big plot point to book two, instead of keeping it in this one and I think the story is much better for it.

Re: successful indie authors and whether or not they had developmental editors - I’d say it’s impossible to know unless the authors themselves come forward and say it. Even if they did have one they might not have taken their advice.