I do not think osta-sarm would replace it because both these sarms are different and have different advantages and disadvantages.
If you want a more aggressive ( because of the androgenic values ) faster acting sarm and do not mind getting some vision sides such as being sensitive to light when coming out of a dark room to the outside or seeing yellow spots then a short S-4 cycle would suit you well.
If you are patient and want no vision sides effects and want to simply set your body on anabolic state then you may want to try the ost-sarm. This sarm is purely anabolic and offers no androgenic effects, sort of like a moderate dose of Primobolan ( methenelone enanthate )
Now, maybe both these be stacked and make a great SARM stack.
12.5mg osta-sarm + 25mg S-4 ?