That's true, but if 10ms gets you 0.001% stale shares and 100ms gets you 0.01% it's still within a good range of acceptance, the difference won't be even noticeable in the earnings.

The point here is that using VPN is not necessarily going to take you from 50ms to 300ms, depending on so many factors as mentioned above the added latency could be too small to be considered, in one of the small farms I have a very poor connection because the farm is located a bit far from the city, I use Ubiquiti p2p bridge to provide internet connectivity, the source itself is rather slow and have high latency because I can only use one shitty ISP, and despite all this mess, my accepted hashrate on the pool is well above 99% most of the time.

In other words, I have more latency than most other people even those who use VPN, so if someone has a fast and solid connection to a good VPN server they will probably do better than me.