Your open-source proxy is decent but it is doing less work than you think, and I would swap it for a sharper test.
Open source protects you from the company disappearing. It does not protect you from the company losing interest, which is far more common — an abandoned repository you technically could maintain is not meaningfully better than a dead product, unless you were going to maintain it, and you were not.
The test I actually use: can I get my data out today, in a format something else reads, without asking them. That covers the abandonment case, the price-rise case and the acquisition case in one question, and it works identically for closed source.
Open source is then a bonus rather than the criterion. Plenty of closed tools pass this and plenty of open ones fail it because the format is theirs even if the code is not.