I would say that moderators get it right most of the times. But sometimes they err, in which case I can think of four routes you can take:

1. Vote to reopen. If the question is very clearly on-topic, it should get reopened rather fast. I agree with your point that

it is much less likely to happen than it being closed by Reviewers, because there is an inherent bias towards leaving a question closed, especially if it has not been improved since being closed.

so this route is not always ideal.

2. Leave a comment in the closed post asking for clarification. Sometimes you might get the moderator to reconsider their decision; if it was indeed a rushed and unjustified closure, I'm sure the moderator will agree and reopen the question. But sometimes the moderator will disagree. In this case, reviewers might read your comment and, if convincing, this will make up for the inherent bias from before.

3. Bring the issue to Meta. If the question was improperly closed, most users will agree with you and quickly vote to reopen. If they disagree with you, there is not much you can do but accept that you were wrong this time and move on.

4. You can always come to the chat, and ask other users (and even moderators) what they think about the closed question. You will usually find several high rep users which can vote to reopen if they agree with you. You can even interact in real time with the moderator that closed the question and they might clear up their reasons (see e.g., this recent transcript where a very similar issue was discussed).

This of course only answers what to do when there are unilateral closures by moderators; I leave it to them (or other users) to discuss whether such a closure is improper or not.

I would say that moderators get it right most of the times. But sometimes they err, in which case I can think of four routes you can take:

1. Vote to reopen. If the question is very clearly on-topic, it should get reopened rather fast. I agree with your point that

it is much less likely to happen than it being closed by Reviewers, because there is an inherent bias towards leaving a question closed, especially if it has not been improved since being closed.

so this route is not always ideal.

2. Leave a comment in the closed post asking for clarification. Sometimes you might get the moderator to reconsider their decision; if it was indeed a rushed and unjustified closure, I'm sure the moderator will agree and reopen the question. But sometimes the moderator will disagree. In this case, reviewers might read your comment and, if convincing, this will make up for the inherent bias from before.

3. Bring the issue to Meta. If the question was improperly closed, most users will agree with you and quickly vote to reopen. If they disagree with you, there is not much you can do but accept that you were wrong this time and move on.

4. You can always come to the chat, and ask other users (and even moderators) what they think about the closed question. You will usually find several high rep users which can vote to reopen if they agree with you. You can even interact in real time with the moderator that closed the question and they might clear up their reasons (see e.g., this recent transcript where a very similar issue was discussed).

This of course only answers what to do when there are unilateral closures by moderators; I leave it to them (or other users) to discuss whether such a closure is improper or not.