^^^^ - We have a couple older apple trees that are 50+ years old. They bear crazy loads one year, and the next - only a few apples. I know some apple varieties tend to be biennial, bearing good crops every other year. I don't know if that can be changed by thinning some of the heavy crop year apples or not. Maybe some of the long-time apple experts can weigh in on altering biennial croppers.
I just watched a video from Penn State on pruning & training apple trees. It talks about pruning to renew old limbs and create new fruit spurs on older, mature trees. ( Which may or may not be 30 footers with heavy wood. Some of their examples looked to be 10 to 15 year-old trees with trunk diameters of around 6" ). I'll have to watch it again to digest more of the good info.
I've also watched some videos from U. VT., U. WVA., Cornell, and U. Mass. where they pruned some old trees to re-invigorate them. Some of the wood they took off was about 4" to 8" in diameter, but they left some upward-growing limbs / shoots to form new leaders with new scaffolds coming off them. The appearance of the finished trees looked much like the pics guys on here post when they graft several scions onto mature trees after they cut bigger limbs off to make the grafts. If your trees are really big and woody, those videos might show you a way to re-invigorate them. I just typed " Pruning Older Apple Trees" in my search bar and a batch of choices came up.