I'd prefer to use layers of:
-felt
-1/8" lauan
-1/2" ply
-1/4'underlayment
to flatten that situation and finish with a complete layer of 1/4" undlerlayment plywood.
Second choice would be to level the whole floor with Ardex K15. That's a process.
Your way can be worked out but it's very unorthodox. When I was apprentice the Old Man use to tell me when I was trying to re-invent the wheel that my ideas were unorthodox. Over time I understood what he meant. After you do it a few hundered times then you realize why things are done certain ways and not typically other ways,