My parents were married in 1968 at the age of 30, relatively late for that time. They were successful young professionals and had only widowed mothers of modest means at the time. So they paid for their own wedding.
Mom was deceased by the time I got married in 1998 at 28 but I'm sure she would have agreed with my dad's sentiment that he would pay for nothing of mine - no rehearsal dinner - nor would he pay for the weddings of my two sisters. His position was that you're grown-ups, not 18-year-olds leaving your parents farms circa 1940.
My old man also gave me a boat load of grief for letting my in-laws pay for my wedding. In hindsight, he was right. I could have - and should have - paid for it. If you let in-laws or parents pay for a wedding, they thus have big-time say over things such as how holidays are spent. My sisters got married at 34 and 39, respectively, letting groom's parents foot the bills, and I've seen how their MILs dictate how holiday time is spent and are generally domineering.
What? How so? First, I can't see a real relationship between paying for the wedding and Christmas plans. And second, even if someone tries to make that connection, someone is free to dismiss it. My MIL bought and arranged the flowers for our wedding and paid for the rehearsal dinner, as well as making the invitations. And if she told me how I had to spend Christmas, I'd laugh and make my own plans. Which I would also do if she financed the whole wedding, or had no involvement at all.
My parents paid for our wedding. It was expensive. They actually upgraded a few items to spend more (the one that comes to mind is upgrading the wine) because they were excited about a big celebration with those who were important to me (and many of whom to them as well). And they have never for one second used that to try and have a "say" over my, DH, or relationship, or our plans. And they never would. They also never really tried to influence our wedding choices. Footing the bill, to them, didn't mean they got to pick the location or veto my dress choices or anything of that nature. It didn't mean they dictated the guest list (though I sent them our list and asked them if there was anyone they wanted to add. I can't recall if they did, but if so, it couldn't have been more than a few people.) Of course, I tried to be respectful of their money and also to make them feel included in the process, since I knew that was important to them (and I'd have done that whether they were paying or not). But they gave willingly and without strings, and I accepted gratefully, and with thoughtfulness and appreciation.
I think ILs trying to dictate holiday time is going to happen regardless of wedding financing. If they are the type to do that, they are going to do it, even if the couple elopes in Vegas. I'm not sure why you tied that to who paid. I have friends whose parents paid for their wedding (and ILs paid nothing) and yet the ILs still try to dictate life choices and holiday decisions. I have friends who footed the bill themselves and still have ILs without boundaries and who think they have a say in the couple's holiday choices. It seems to me that this is a common phenomenon, and there is no correlation at all to wedding funding.