Ok. You’re attempting to analyze carpentry when you have no experience in carpentry. Forget all the online “resources”.

Forget messing with the substructure which is part of what holds the shed upright.

Layer 5/8” exterior grade ply at right angles to the existing ply. Use construction adhesive applied in lines approx every 12”, drive deck screws onto the substrate and 2x4s. Paint with garage floor paint.

Stop watching DIY youtube by people who know nothing.