It's not really wrong. There are English accents (such as Received Pronunciation) where an "ee" before an "r" is normally pronounced with an [ɪ] like in "wit". In any case, even if you pronounce the "ee" as something else like [i], "Veert" is probably still the sequence of letters that maximises the likelihood that an English speaker will understand by it something close to the true German pronunciation ([vɪʁt] or [vɪɐt]). "Virt", for example, would be read by most people as [vɜrt] (rhyming with "hurt") which to my ear is further off from the correct pronunciation compared to something like [viət].

"Veert" is correct, in the sense that it's how a German would pronounce it. Of course, the great man wasn't German; I don't know how he pronounced his own surname.

"Wit" is just wrong. Perhaps that was a joke that I missed about the man's humour.

The "i" sound in "wit" does exist in German and is what is normally indicated by "i" on its own. The long "ee" sound is normally spelt as "ie" in German.

We have both, and I'd tend to pronounce "Wirth" similar to "wit" as far as the "i" goes. It's not always clear just from looking at the letter. But some words have explicit cues: There are "stretching consonants" like a-a, a-h, e-e, e-h, i-e, i-h, etc: Aal, Kahn, dehnen, dienen, sühnen, etc. And sometimes the following consonant gets doubled up to indicate a shorter pronunciation, like in "Bitte".

And what's the difference? AFAICT it's pretty much exactly the same sound, except in one case it's longer, in the other shorter. Say "bit"... Then say it again, only looonger... And you get "beet". Say "wit", but longer, and you get "wheat".