Maybe it depends on your origins or age, but I'm over forty and attended a conservative religious school, and it boggles even me that anyone considers "he" the current generic/default pronoun.
"they gives me the shivers"
Grammatically, the "they" is clearly plural, as it is used with the plural verb form "give" and not the singular "gives".
Look up "subject verb agreement".
It reminds me of the time I recommended (to the Unix team at a major financial institution) that they use ssh rather than telnet, and being rebuffed with "that's the way we've always done it".
In this case, since you want to be specific, the practice of defaulting to "he" correlates with hundreds of years of treating women as chattels, with economic consequences and imbalances that persist today, and continue to be reinforced through structural, unconscious, and explicit biases, and that we'd all be better off without.
The notion that language should reflect thought is as old as Plato.
Er, no. It just means it is the unmarked/unremarkable case corresponding to males being generally worth less and discardable ("save the women"...).
It is also a quirk of some of our languages that the gender-neutral pronouns are considered derogatory when applied to people. German and English have this problem ("it", "es"), whereas French "on" seems to be okay.
So the language requires gendering when no gender is semantically intended. In German, every noun is gendered. So "person" is "she", whereas "human" is "he", "Civilisation" and "Society" are both "she", "state" is "he". "Lampshade" is "he" whereas "Lamp" is she, etc. You can try to read deep meaning into these quirks, or you can just not.
TL;DR: Not only are you reading way to much into linguistic quirks, your analysis is also at best shaky.
I also find it weird that German and Spanish inject gender into every noun, although I do get that there's little meaning behind it (from the little quizzing I've given speakers of each)
Yes, language evolves. Currently, this is almost certainly grammatically incorrect, "they" being the third person plural and (not shown here, but assumed) the speaker being singular.
"They" is being pressed into service as the non-derogatory, gender-neutral third person singular that's missing in english. So "they" has started to mean both third person plural and unspecified third person singular. The previous solution was that "he" meant both "male" and "unspecified". So previously women got their own pronoun, men didn't, now we have a harder time telling whether there's a single person or a group.
Both solutions have their quirks, both work at some level.
"As long as they give a good talk" - you're not talking about one specific person but in fact a general population of speakers.
The pronoun refers to "speaker", singular, yet indefinite, we don't necessarily know who it is.
Let's substitute "they: "problems a speaker at a conference might have, as long as they give a good talk/presentation."
Yep, works for me, but I think the "they" definitely talks about about that single (if indefinite) speaker. Yet we use the plural of the verb ("give"), so the sentence is confused, grammatically. I wonder what will give as this evolves, whether "they gives" becomes acceptable or we simple leave "they" grammatically plural even when it is semantically singular.
Language. Fun times!
"They" has been grammatically correct for single person of unspecified gender for hundreds of years. Do a little research before saying ignorant things.
I think that's what I wrote.