I think it might suffer from confirmation bias. Say Dropbox started in Milwaukee, WI, but was convinced they needed to move to San Fransisco to be successful. Maybe they would have been successful in Milwaukee, too, but now we'll never know. So now they're contributing to the startup successes that come from SV, but that doesn't necessarily mean that SF was what made them successful. Maybe the reason the parent thinks Boston's startup scene is dying is because people who create startups are leaving to move to SF because they think they have to.
Maybe the number of success stories coming from SF has more to do with the sheer number of businesses that are started there? If 100 businesses are started in SF and only 5 in Tulsa, even if only 10 of the startups survive in SF while all 5 survive in Tulsa, people would still say "SF has twice the number of successful startups" even though 100% succeeded in Tulsa vs just 10% in SF.
DropBox is an ironic example because it actually started in Boston. Drew had grown up knowing VCs in the Boston area; some had even told him "If you ever start a company, we'll fund you." DropBox did the YC Summer Founders program, which at the time was located in Boston, but all the Boston groups also did a demo-days out on the west coast because Silicon Valley VCs were better. Sequoia gave them a term sheet within a week; all those Boston VCs that Drew had known forever dragged their feet and were like "Is there any money in sharing files? There are literally dozens of competitors, and none of them are making serious money", and that is why DropBox is in San Francisco.
I grew up in the Boston area as well, thought I would stay there my whole life, and a lunch conversation with Drew was actually instrumental in changing my mind about moving to Silicon Valley. The reason is precisely that: the Boston business climate is so conservative that you really can't get resources unless you're working on something that has made money for other people. I actually don't think I'd start a company in the Bay Area now if I didn't already live here and have a wife with family here - there's usually a long period of learning your market before you have anything fundable, and it's better to spend that in a region where rent won't cost you a fortune. But the Bay Area remains the best place, bar none, to scale a business, and it's quite likely that if your nascent business has any serious growth potential, it'll be fodder for a Silicon Valley competitor with $100M in funding.
This is the most spot-on reply to my comment ever. YES. A thousand times YES. THIS is the problem with Boston. It's probably a fine place to start something. But an almost impossible task to get it funded and supported. This is why I think it's on the downward path. Boston VCs are ridiculous.
According to WalletHub, SF rates pretty darn far down the list of best places to start a business: https://wallethub.com/edu/best-cities-to-start-a-business/22...
Maybe the number of success stories coming from SF has more to do with the sheer number of businesses that are started there? If 100 businesses are started in SF and only 5 in Tulsa, even if only 10 of the startups survive in SF while all 5 survive in Tulsa, people would still say "SF has twice the number of successful startups" even though 100% succeeded in Tulsa vs just 10% in SF.