As your definition notes the term is derogatory so yes it does imply some element of one being misled as if they were happy then they would have no reason to use the word womanizer. They would instead say ladies man as there are no hurt feelings.
And there is no real evidence of Gambit being a womanizer. He has been with Rogue for much of his time with the X-men and in fact Rogue has had more relationships with known characters than Gambit.
Nor are the Frenzy or Storm relationships evidence of his womanizing because he refrained from progressing those relationships. An actual womanizer would have actually slept with both of them. Gambit did not. Not to mention Frenzy only kissed him to try and get over Cyclops whom she was in love with in the Age of X storyline just as Gambit could be said to be trying to get over Rogue. So that was not an act of womanizing. It was two people trying to forget about an ex.
So I think the label doesn't fit. Gambit simply hasn't slept with enough women over the years for this to qualify and is being judged more harshly than women doing the very same thing.
Derogatory could also be as a result of social constructs frowning upon the behaviour. Take slut as a similar example it is derogitory with a similar definition with no deciept involved.
It is such a fickle thing so much grey blurring black. But the thing with casual flings are at somepoint you are bound to have sever emotional casualties. Esp if one is more invested, heck he became one to rogueneto. I tend to believe one should be caeeful with others hearts because you never know when it wont just be a casual thing to another. Heck it might start that way and explode horribly how many friends with benefits relations exploded for exactly that reason someone became more invested.
With Storm it may not be there but when she acknowldeged that it would likely upset Rogue it implies she maybe felt more about it than a passing pash. I think if they started sleeping together there is tonnes of room realistically for it to imploded and leave chaos in its wake.
Frenzy is a lesser example she was clearly disappointed when she left if it had been more then what when he wasnt invested fortunately he didnt take advantage. But he was rruely loving in that moment he could have rebounded with her and left her hurt maybe you could write it loke its all sunshine and daisies but may not make sense.
Any way it good to debate alternate world views.