The question isn't really whether it's ok it's whether M F-35's are better than N alternative fighters at some task, for M<N.

A problem is that it needs to replace a lot of different planes (a-10, f-18, f-16, harrier...) and those have different roles. It's likely to suck royally at replacing the A-10 for example, or to act as an interceptor for defending the airspace Norway and Denmark which have no alternative fighters to back it up - but if a decision is made to e.f extend A-10 life, or buy a light attack plane for that role, then F-35 numbers go down, and unit price up.

Basically the F-35 has to be bought to do things it doesn't do very well or very cost effectively because otherwise not enough will be sold for it to be economical