If you're measuring argument "strength" logically, the first paragraph is false; and if you're doing it rhetorically, it's misleading.

On logical grounds, insults neither add nor subtract appeal to the argument. That can be seen in the example: at the core, the argument in the bottom left could be rephrased to remove the insult, and it would still convey the same reasoning. Emotional factors shouldn't be considered on first place..

And, on rhetorical grounds, insults can weaken or strengthen a position depending on the claim, context, and audience. (A good example of that would be the old "fuck off Nazi".)

for those who recognize frustration reactions as a sign of weakness. [plus the second paragraph]

This is an audience matter, so it applies to the rhetorical strength of the argument, not the logical one: I don't argument for the sake of assumers, and claims to recognise frustration out of how others convey an argument is assumer tier irrationality. As such, even if insults would weaken the argument for them, I don't care.

In fact, they're perhaps the major reason why I personally would recur to insults - to discourage their participation, since assumers are as much of a burden as sea lions (for roughly the same reasons).

If, however, you do argument for the benefit of this sort of trashy individual, be aware that even the assumers might react positively towards insults against a third party. Some will make shit up that you're "weak" and "frustrated"; some, that you're "strong" and "brave". It'll depend on the general acceptability of the claim that you're making on first place.