Nope. Alt is kind of more important to give users a bit better chances when searching images, but filename is the important one, but the most important thing is to use right context, ”this an apple: <image of apple named apple.jpg, alt is apple>.
Alt text is very useful for those using screenreaders - including people who are blind or partially sighted. But ideally it is text which describes what is being shown. It’s an accessibility issue. (I can’t think of a simple way to do that annotation - one of the image-oriented software services might do it.)
Of course it is. Well, more or less the argument is anything else than SEO.
I have two blind friends. Both are saying same all the time: the issue is not alt itself, but lack of quality alt-text, plus using alt everywhere all the time on images without any content — and here I see really big issues when webmasters get AI that starts generate alt-texts.
And… the main issue for screen readers is bad design of platform, and there the team has done quite good job.