Basically what I mean is - if it can do what it's meant to do - go to Mars - then it's also an easy space station replacement.

You can argue if it will get to Mars of you want. But silly to argue that anything that can get to Mars with human occupants won't be able to also orbit the earth with human occupants

It's as silly as it's to argue that good off roading car makes also a great grand touring car.

Sure, it may, maybe. But those are 2 very different use-cases, and it's not given or easy by any way.

At the same time it's much more likely that a company that makes rockets that do one thing would also make rockets that do another thing much more easily and faster than a company that does not make rockets at all.

For example Ford makes cars and trucks.