Arial isn't really a true Helvetica knock-off,
although it does deliberately copy the metrics of Linotype's first Helvetica digital font files. More on that here:
www.marksimonson.com
Rather than be a Helvetica look-alike such as Swiss 721, Nimbus Sans or CG Triumvirate, Arial is more of a Frankenstein's monster hodge-podge of styles. There is some Helvetica in there along with bits of Akzidenz Grotesque, Bell Gothic and other sans typefaces.
It's pretty easy to spot the visual differences between Arial and Helvetica. I think Arial has a pretty harsh look to it due to all the odd angled cuts and sort of crooked flow of its letter strokes. The 1957 cut of Helvetica has some of its own ugly-ish problems, which were cleaned up in the larger and more useful 1980's Helvetica Neue super family. Further improvements were made with Helvetica Now, first in 2019 with a series of static display, text and micro styles, then in 2021 with a variable version. I think Monotype may release a second variable version. The current one has a variable width slider that goes from standard width to compressed. They need to make another version going from standard width to extended or wide.