You get different things from pair programming compared to post-completion code review. They share some benefits and to some extent can compensate for the lack of each other, but ideally you want both.

If you're reviewing someone's code at the code review stage, you can only do so much. If it's working, tested code then asking for major changes is either pointless or very costly; there's little point in suggesting out a better way of approaching a problem if it requires major surgery. Unless you spot a potential bug or something that will cause major problems, you're realistically restricted to suggesting minor changes like style suggestions or better names for things.

With pair programming you have two people collaborating on a design from the start where suggestions for better ways of doing things are much easier to incorporate. If pair programming for a complete feature is either not feasible or undesirable for some reason it is at least often worth pairing to start a feature off.

Code review on the other hand also has some benefit in getting a fresh pair eyes on a piece of code to spot obvious mistakes that people elbows in deep in it have glossed over or find hard to see, such as left-in debugging code or user credentials.