The real problem is network effect and collective action.
Whether it's whitelisting, "impact factor", or whatever, lots of tenure committees will have evaluation criteria you have to meet. So in that sense you are very correct.
What misterdoubt was saying, I think, is that nobody in the field actually actually cares that it is Y Journal of X, what they care about is who is publishing in it. Elsevier or whomever isn't what makes it a high impact journal, it's the papers and researchers.
So while what you say is true, it's also true that if everyone in a field could mostly agree to drop Y Journal of X in favor of X letters, or whatever, it would work fine and the tenure committees wouldn't take long to catch up. There might be a year or two of confusion, but that's it.