If a player scores 60 goals in a scoring environment of about eight goals per game and another scores 55 goals in a scoring environment of about six goals per game, the latter player's goal scoring is more valuable in the sense that he probably helped his team win more games and pick up more points with his scoring.
But did he play better? That's not necessarily the same thing. That's where things like efficiency of scoring, opportunities given, teammate and linemate quality, all-around play come into the question.
I don't think HR's adjusted totals are meant to try to determine if a player played better than another. They just give relative value to goals and points. Like currency, these things do not have a fixed value. 50 goals in one season isn't the same thing as 50 goals in another.
I think the main issue is most people (myself included) try to use adjusted scoring in a much broader way than it's intended.
Sticking with your example - it's literally true that 55 goals in a 6.0 GPG scoring environment is 22% more valuable than 60 goals in an 8.0 GPG scoring environment. It's simply a mathematical calculation.
The challenge is, most people here are interested in the performances of the league's
best players. It's literally true that a goal in a 6.0 GPG league is 33% more valuable than a goal in an 8.0 GPG league. But that's based on everyone's collective output - superstars in their prime, middle-six forwards, goons and grinders, stay-at-home defensemen, and offensive defensemen. Everyone wants to know how Ovechkin, Crosby, and McDavid stack up against Hull, Beliveau and Jagr. Not many people really care about how Niklas Hjalmarsson's offensive production compares to Adam Foote's, or Craig Ludwig's, or Bob Goldham's.
In other words - adjusting based on the league average, strictly in a mathematical sense, is perfectly accurate. However, it can be outright misleading to focus on the results of star players, because how much a star forward (or offensive defenseman) produces depends on many factors. The past few seasons haven't been particularly high-scoring by historical standards (measured by goals per game), but top players are scoring a lot due to more PP opportunities, more teams have good puck-moving defensemen, the existence of 3v3 overtime, and teams pulling their goalies earlier and more often. Each of these factors favours top scorers. Your stay-at-home defenseman playing 15 minutes a game on the third pair isn't going to benefit from any of those changes, but McDavid, MacKinnon and Kucherov will. That's why this season only features about 2% more GPG than 1965-66, but there are 12 players scoring 1.20+ PPG this year, compared to just one in 1965-66.
There are issues with VsX (which I've written about in other threads), but it's primarily focused on how the league's best players perform. That makes it better suited for the cross-generational Karlsson vs Coffey type of discussions. VsX is probably less accurate if we're comparing the offensive production of Doug Jarvis vs Stephane Yelle, but in my experience, nobody is overly interested in that.