Your experience isn't that uncommon. I've had both a truck parts store AND a mechanic who said he builds custom suspensions both say, "I've never heard anyone tell me they have problems with spacer kits". Sure, maybe they haven't. But they also probably don't research what others outside of their offline community have to say about it. I'm sure there's no shortage of shops or mechanics who's only feedback is local and don't go on the internet. The mechanic I spoke with just gave me a look that basically said yeah sure, whatever you want and obviously wasn't interested in what website communities had to say about Bils vs spacers
On the other hand, when you're on the internet, people don't tend to show up for no reason at all just to tell everyone "I've had Bils or spacer blocks installed for 5 years with no problems". People tend more to post when they're having issues, not the lack of them.