And it does serve a purpose: giving weapons cool, flavorful, and importantly limited usage/small effect abilities. Of all of Larian's homebrew, this is one of the best in terms of coolness-to-OPness ratio.
Coolness is fine; but make the characters cool, not the weapons. Most of Larian's homebrew is about taking cool things that maybe a character could do and instead baking it into an item.
Characters in general cannot cleave in 5e. The only one who can is a Hunter Ranger who took Horde Breaker, but they can still do that in BG3. Thus, Larian isn't taking anything away from the characters.
Are you arguing that Larian should instead add a "Cleave" feat and/or ability to the Fighter class? I'm not opposed to such a change in principle, but then we'd run into balance problems that I don't trust Larian to do properly. If the Cleave feat was usable 1x per short rest, it'd be a waste of a feat. If it was usable every turn, it'd be way too powerful.
