Couldn't have said it better.
If it was not RNG, I wouldn't mind even a much higher cost than previous souls (they were usually under 200 vials each tier), let's say 600 vials from 13 to 20, would still be reasonable (no rng)
But now, you have this rng system to hide the fact you need about 3k sacred oils to max soul and roll good stats on it. If what NCSoft aimed for, is only lucky people to continue playing (that need far less than thousands cuz lucky), then you achieved it, but don't be surprised while everyone else leaves in frustration.
Anyway yes the damage is already done and most probably too late to fix. This needs an emergency fix, remove the RNG, make it a reasonable cost (like 500-600 vials to +20), and compensate the people who already tried on souls with stuff back, but this is the issue. This patch should've never been approved this way.
EDIT: This applies to gold costs on weapon / accessories too. The insanely low RNG chance is there to hide the fact it costs millions of gold to max them. Again, if there was no rng, and people saw the costs, they'd immediately quit. IF what NCSOFT aim for is only lucky people to continue playing, then have fun with 1/10 players of an already low playerbase.