What are the drawbacks of Librewolf compared to Chrome/Safari or even compared to regular Firefox?
Discussion
LibreWolf is all advantages
Lobrewolf is a hardened fork of Firefox, which just means it's already configured for security.
So your drawbacks vs chrome are any perceived drawbacks of Firefox vs chrome, which tends to be that some websites choose only to optimize for chrome so some of their features just don't work properly on Firefox variants.
Drawbacks vs standard Firefox (assuming no hardening) are simply sacrificing convenience for security. You'll find that some pages break because they're unable to perform careless behaviors such as cross site requests or feeding you potentially harmful cookies.
There's nothing that Librewolf does that you cannot do with Firefox. Librewolf just does it for you out of the box.