です is actually thought to be a contraction of でございます (and ます is thought to come from 参す but that’s neither here nor there) so I’m definitely not confusing those two.
But no I’m not “hung up” on it, and Bunpro is not the authoritative source on Japanese etymology.
But also, couple of things about English, since you’re making the comparison: its primary copula, “to be” also means “to exist.” The words are very close in this sense.
Also, similar to Japanese, English does not have a future tense. We use a present tense auxiliary verb (‘will’) to talk about future events. It’s simplified and referred to as a future tense in the classroom, but it’s actually a grammatical aspect. If English had a future tense we would say stuff like “I runnill” (pretend -nill is like the future tense version of -ed). But yeah, English is a Germanic language, and none of those bad boys have future tenses.