Is it polite to reply the email and point out that i had the same role
before and my employers were more than happy ? or it wont make a
difference ? i'm afraid that it might look rude.
It's not rude, it's just usually a waste of time.
It sounds as if you are imagining that replying to a rejection letter and pointing out where the rejecting company was "wrong" might help you change their mind.
Unfortunately, it pretty much never works that way, in my experience. I've interviewed, and rejected, more candidates than I can remember over the years. I've had several folks who contacted me after being rejected, trying to plead their case. I've never - not once - changed my mind and accepted a candidate that I had already rejected.
Companies typically interview at least several candidates (and sometimes many) for a given position, then choose one above the others. They have far more complete knowledge about what they want in the role than you do, and they get to judge how well each candidate fits. Unfortunately, they have concluded that you aren't the best fit.
Sending rejection notices is basically a formality on their part. They are always sent using very general language and no specifics.
While the rejection you got might say "they are looking for someone that has in-depth knowledge in the field", the truth is that they found a candidate who was more qualified than you are (or at least believe they will find a candidate who is a better fit than you are). There are almost always a variety of factors making other candidates superior, and in-depth knowledge may be part of it, but there may be more to it. The rejecting company won't go over each and every detail about how they made their decision.
Pointing out that (at least in your opinion) you do indeed have in-depth knowledge in the field, won't change their mind. While you may have depth, another candidate might have more depth. Or other factors may have tipped the scales. Pointing out your depth now won't make a difference to the hiring company once their decision is made. The time when that would matter is during the interview, before the decision was made. It's over now, and it's time to move on.
I know it can be frustrating to learn that you have been rejected, and not have deep insight into why. But unfortunately, that's the way it works.
Keep up your spirits and your job search. I'm sure you'll find a position that meets your needs and for which you are the perfect fit.