The strength and skin appear to be up to par with the powers they have.
A person with super strength would need skin that's strong enough to not tear apart when lifting a literal ton over their head, or when they punch through a concrete and steel wall as is often the case in a Supes' profession. A person who swims deep in the ocean needs a body that's resilient enough to withstand the pressure of the deep ocean. A person with superspeed needs to be able to withstand the air resistance as well as all the bugs they're sure to run in to which are basically bullets. These added resiliencies will have carry over to other things like being bullet or knife proof.
They could have alternate explanations as well, for example in the DC universe, speedsters have a "Speed Force aura" that protects them and the people around them from harm. These are never explicitly mentioned (yet). Though the Supes' powers are generated by a drug and not some external force or deity, so being ultra-resilient would fit more.
In the case of Translucent, he's unique in that his power doesn't require added resiliencies. However, the Boys and other Supes throughout season 1 go out of their way to mention that he has impenetrable skin which would imply that it's not standard. They never state that he has impenetrable skin because he's a Supe. So his skin seems to be exceptionally strong even by Supe standards.
Mesmer is one example of a Supe that doesn't have any enhanced physical abilities. We know this because:
Mesmer is easily beaten to death by Butcher who is a normal strength human.