Unless their local client was compromised (not impossible - but if your local is compromised you're in trouble regardless), even if someone hacked them and stole their data, they would not have your clear-text info.
It's everyone's choice to make but I am personally OK with this security/convenience trade-off.. It's "good enough" for me - mostly because I trust them to know how to do this better than I could - if it means I can manage all my passwords in one place and access them from any device.
1Password also has useful (to me) quality-of-life features like integration with HaveIBeenPwned, it can also show you re-used passwords, and if you store credit cards or other info, it will also tell you when they're about to expire etc..
Plus you can store any arbitrary metadata with any record, so I even use it to store non-sensitive, but still private, info associated with logins, docs, ID, etc..