Kinda "meh" on this one. Sure, attackers will use other formats to spread malware. But, it's not like thy haven't been successful enough with zip files. If anything, it might mean that Windows Defender actually has a better chance to analyze the contents, before they execute. Though, whether or not Defender will actually block the execution is open for debate.
Another perspective: do you trust the average consumer to ever update WinRAR or 7zip? If it's baked into Windows, at least Microsoft can patch any exploits that are discovered.
I turst application's auto-update more than users complying with windows updates. They tend to disable windows updates because "they are anoying, long and supposed to add more bloat and bugs and I never reboot my PC".