Well with experience of being bitten three times in my life.... they are worse. The reason being is that they can be easily provoked and if they feel like their space is being evaded they will come after you. And with that, signs show up within a few days, and you can never know unless you've been bitten quite a bit of times.
I've known some who have let it go for so long they had to amputate legs, arms, fingers and so forth. others, ive know as ******** and elderly people die from them. They are worse than a black widow because of that.
Black widows, if you leave them alone, they leave you alone basically. Ive been around both for about 19 years and was never bitten by a black widow.