Interesting experiment! I ended up here when Googling for more information about whether or not vaseline would be bad as a component of a specific leather balm I had my eye on (Urban Forest Premium Leather Balsam, which I wanted to get as alternative to Obenauf Heavy Duty LP which isn't available here). I had already looked for what were 'good' products vs 'bad', with anything petroleum based (including vaseline) most often being chucked into the 'bad' pile. But that balm also has beeswax, avocado oil and other natural oils in it, besides vaseline. Reviews on it are excellent, as is 'picture proof', but still I was concerned.
While not conclusive/100% scientific yet, the rational debate and testing in this thread has at least given me a bit more peace of mind about potentially using that product; since it's not pure vaseline and contains natural oils and beeswax as well, there's a good chance it's a 'healthy' balance between them all and it might not long term deteriorate the leather (at least that's what I'm telling myself, since I couldn't find another product here that guaranteed only mixes only natural oils and beeswax, and making my own is not an option). It's also not like I'm planning to treat heirloom pieces with it, just some knife sheaths and revive/condition a few leather belt satchels. But when there's doubt, my mind tends to go down rabbit holes.
So thanks for your efforts, adding actual valuable info to the interwebs rather than just echoing/parroting (unfounded) hearsay.