Replacing water damaged Cresdeck D-3
here a common construction is 1/2 or 5/8" plywood or more recently 23/32 OSB.  Both are often rough.  Next layer in cheap construction is some form of particle board, then carpet over that.  This, especially if done with cheap carpet is the lowest cost way to do a floor.

This substrate is also ok for laminate floors.

If you want to put down vinyl sheet flooring you need to upgrade the surface to something smoother, although there are now loose lay vinyls (thicker, stiffer) that do just fine on an OSB floor.

If you want to put down tile (I like tile for areas that get wet) then you need a thicker foundation to lay tile on.  In my laundry I bent the rules and used that same 23/32 OSB on the 5/8 plywood first layer giving me 1 3/8" total sub floor on 12" spaced joists.  The OSB got 2 coats of white paint to seal it, then I laid 12" tiles on it in a running bond pattern.  The floor has been zero problem now for 14 years.  (Tile doenn't bend.  Easy bend test.  Put a pie pan of water on the floor.  shine a flashlight on the pan from some supported point.  Look at the refected spot.  Now walk.  If the spot goes crazy, you need to consider a different flooring option.  Repeat the test at a friends house who has a tiled floor.  See the difference.

Your best solution would be to replace the soggy bits with exterior grade plywood, then use a water resistant top layer such as loose lay vinyl secured at the edges with double sided carpet tape, and a bead of silicone caulk on the perimeter of the room.

A cheaper solution would be to use 90 day exterior rated OSB, and a decent brand of vinyl plank floor.