I'm going through this exact same thing right now and I'm at five quotes. Here's what I've found:
They can't "require" bundling, but they can make the tied pricing their only competitive option.
The best three quotes for me all came in bundled. State Farm, American Family, and Travelers were all close and with agents I know. Liberty Mutual was the highest.
Geico was the cheapest on car insurance, but any of the unbundled homeowners options would have negated their savings. I've also been hit by a Geico driver and I wasn't treated well by the company. Just bad service by multiple people.
I then priced out adding an umbrella and it'll tip the scale over to Amfam. They're just under the other options and the agent is good.