Sola scriptura means that everything is tested by Scripture. That’s a bit different than saying that everyone starts from scratch to develop their own theology from Scripture. There is theological tradition, based on theological scholarship. At least in the confessional churches, this fact is acknowleged.
What sola scriptura does is say that in principle all theology has to be supported by Scripture. So you can always challenge tradition. In principle this means that Protestant churches can correct themselves more easily than the Catholic tradition. How well that works out in practice you’ll have to judge for yourself. I tend to be a bit skeptical. I think it’s a good theory, but it’s not so often practiced well.
If things were working properly, we should see a single Protestant tradition, or maybe a few major traditions, making continuing adjustments in theology. In practice there are some groups that work that way, but the usual reality is much messier. Changes tend to happen by creating new groups, not by continuing reformation of existing ones. And new groups seem to happen as often due to someone’s hare-brained idea as genuine new understanding.
I’d claim, however, that the mainline churches have done a reasonable job of implementing the stated strategy. They have been willing to change, but change has generally been based on real new scholarship. An encouraging sign is that those changes have tended to bring the major traditional theological approaches together.
