The author clearly made the claim that group G suffers especially from problem P. Your counter was, "Why don't you say we should help everyone with problem P?"

This is exactly the form of black lives matter answered by all lives matter, which is well-known by now to be a poor argumentative form. It's a poor form because the point of raising problems is to direct attention to where attention is most needed, but you're not actually addressing whether or not attention is most needed there--you're just attempting to dilute attention without justification.

You could have disputed that G suffers disproportionately from P. That at least would have the form of a good argument (disputing premises). (Whether it was good would depend on whether you could make a compelling case that the premise was wrong.)

You could have argued that despite P being a problem, it's a pretty small problem in the grand scheme of things, so we should keep our attention elsewhere. This also has the form of a good argument (because it contests the implicit premise is that G suffering from P is worth attention).

There are probably other options. You seem to be referencing some sort of privilege/oppression argument in your reply, but you didn't make that in the original, and you didn't make it this time either, just suggested that such an argument is so clear that it's "outrageous" to not understand it without being told. So it has the form of a good argument, potentially, but wasn't developed into an actual good argument.

But the one you actually went with doesn't even have the form of a good argument.

(In case it's not obvious, one wants to make good arguments because all we mean by a good argument is "if this, then that, so if you believe this and not that, things are not going to go how you expect". Good arguments reliably reduce confusion, in-practice hypocrisy, and self-defeating actions.)