Recently, I have submitted a paper to a high rank journal where I have considered a physical system, and applied a mathematical technique. In order to perform this technique, I have considered some approximations, and the results obtained extended previous results. However, the approximations used in the paper are valid among different approaches in the field, being used in different papers. From this perspective, I know how to response to the referee critics, with evidence from the scientific literature. The question would be if it is appropriate to respond to the referee critics and to motivate in the article the mentioned limitations, or to submit to a new journal. I mention that in the previous published papers by our group the referees didn't used the word rejection, and have pointed to a major/minor revision. Note that the reviewer report does not says anything about the invalidity of the results, only that they are limited by the approximations used in order to treat the system mathematically and not numerically.
Update: the paper was finally rejected. The reviewer's comment from the second round were not so negative, recommended a major revision, but the editor decided to reject the paper.
New update: the referee comments from the second journal have arrived, the paper has a high chance of being accepted after a major revision. Eventually the paper was accepted.