delaminated?

an area of floor by kitchen sink has delaminated so sags as its stood on.
My thoughts are to drill out excess foam exit holes in pattern shown online and instead of an expensive delamination kit is to use, surplus to requirements, builders spray on/in foam generally used for filling gaps in window and door frames, and has its own adhesive capability.
ALTERNATIVE:
1 Cut out and remove delaminated area
2 Cut& fit builders insulation polystyrene.
3. Fit insulation sheet after applying contact adhesive .4fitto base then top when in position
4.coat new 3mm ply board when tacky fit in position, level out to existing floor.
5. fill gaps as required.
What say you?
Good or bad but clean comments/ advise