Lock files also remove the "silent security fix" that was touted as the benefit of other systems.
You can't have it both ways.
You either get reproducible builds (by default with vgo, by adding lock files in other systems) or you get silent upgrades that potentially fix security issues (but also potentially introduce security issues).
You also mis-characterize the position of vgo creator. He doesn't think that lock files are a huge issue per se.
The difference is in default behavior of the system: vgo by default picks predictable, consistent version of dependencies. That version doesn't change if dependencies release new versions.
In fact, it's not just the default behavior but the only behavior.
Other systems allow specifying complex rules for which version of dependency to pick and they all allow for a scenario where you run the same algorithm over the same rules but pick different version because in the meantime some dependency has released a new version.
It's such a big problem that all those system end up introducing lock files, which is a tacit admission that what vgo does by default is a good idea.
vgo doesn't need lock files to get the benefit of lock files, which is a nice cherry on top but the real advancement is in changing the default behavior of how resolving versions of dependencies work.