Ivan Vegvary wrote:
Finally had an occasion to use my oscillating tool. Cutting 8"x16"
holes on the underside of my eaves to create ventilation. 36 total!
3/8 inch plywood boxed eaves. Considered skill saw, saber saw, roto-
zip and oscillating tool.
Note: This is all overhead work, approximately 8-11 feet off ground.

I had almost the exact same project except my holes for soffit vents were 8
inches by four feet. I tried several of the same tools you did.

What finally worked best for me was a branch-trimming chain saw!

Oh the edges of the resulting hole were not, er, "neat," but they were being
covered by a home-made screen, so the irregularities did not show.

And, as another responder said, you CAN "sharpen" a worn-out blade by using
a rotary Dremel to cut as many 1/8" slots in the blade as you can muster.