I don't understand why people don't just read Google's own published guidelines ( https://developers.google.com/search/docs/fundamentals/seo-s...) on how to properly SEO one's site.
It's not some dark art. Google themselves tell you exactly how they index and why. All you have to do is read the guidelines.
I did this during a migration of a site that used '/<pk-int>/' and was changed to '/<slug>/' with corresponding 301. The SEO not only didn't punish the migration, but it seemed to like the change (except the Bingbot, that after five years still request the old Urls).
The problem I see with the OP strategy is that the bot can hit a Url that still doesn't exist, get 301'ed with that technique, and the Url is reused afterwards for new content: following their example, somebody links to '/supplements/otherbrand-spore-probiotic', that gets a bot following that link 301'ed to '/supplements/spore-probiotic'. Later you actually add 'otherbrand-spore-probiotic', but that Url will never be visited by the bot.
[1] https://developers.google.com/search/docs/fundamentals/seo-s...
This reminds me of something similar in the mobile world: Apple's App Review guidelines[1]. They're surprisingly clear and to the point. All you have to do is read and follow them. Yet, when I worked for an App developer, the product managers would act as though getting through App Store review was some kind of dark wizardry that nobody understood. Them: "Hey, we need to add Feature X [which is clearly against Apple's guidelines]." Me: "We're going to have trouble getting through app review if we add that." Them: "Nobody knows how app review works. It's a black box. There's no rhyme or reason. It's a maze. Just add the feature and we'll roll the dice as usual!" Me: "OK. I've added the feature and submitted it." App gets rejected. Them: "Shocked Pikachu!"
I'm with your colleague on this, at least in a historical context.
I was also well aware of and accepting of the risk in my case. I wanted to learn more about certain iOS features, and I was able to do so scratching an itch I felt like scratching. I would have still gained from the process even if it had been rejected. However, as it got approved, contrary to the guidelines, I also got a good laugh at how inconsistent review was and a nice cash bonus on top!
You win some you lose some. Such is life.
Going through any forum thread of "reasons you've been rejected" and trying to find the reasons here isn't obvious.
I couldn't find anything in there pertaining to why we were rejected last month (mentioned Android in our patch notes as it's a third party device we integrate with).
301s are what you are supposed to do with things like changed URLs, so I cannot see it being a problem in this case. A 301 is nor duplicate content - it is one of the things Google likes you do do to avoid duplicate content.
It would probably be good to add a threshold to the similarity to prevent urls redirecting to something very different.
Semantically, using a 303 redirect might be the most appropriate signal for what they are doing.
They could redirect to a specific result page if it's a clear, unambiguous match and they could redirect to a search results page if there are other possible matches.
Then there are the vagueries of a search engine becoming ever more dependent on ai where not everything makes rational sense and sites can get de-indexed at the drop of a hat.