He's also ignoring that the operator of the platform is only interested in OpenBSD, whereas on Vultr OpenBSD's ability to run could disappear at a moments notice.
If they remove the ability to work with a custom ISO they would be putting themselves at a severe competitive disadvantage to literally every other competent VPS provider on the market. Doubt they have that in their strategy, I feel it's important myself to be able to partition how I see fit for example.