Doesn't the fact that they reduced RDM MP costs across the board already prove their point?
No, it says that they agree with the common perception that RDM MP expenditure is too much. It still says nothing about what you're "supposed" to be doing with Lucid.

Lucid has the sole purpose of restoring MP, so if you need MP, you use it. If you don't need it, you don't. Any arguments over whether you "should" have to use it or not are irrelevant.

RDM got the mana cost changes to its ST rotation because the math stated it bluntly: with perfect 100% uptime of LD the standard rotation had a maximum time limit of 15 minutes.
Which is more than good enough for any fight in the game. Any fight that lasts longer than this either has forced downtime/recovery periods (hell, most fights that don't last that long still have them), or has severe enough other problems as it is with the party in question.

Regardless of skill level this is what the math said. Personal experience did not matter, this is what the math and the logs stated.
Personal experience does matter, though. Do you think I'm going to be all like "well, I should be out of MP right now according to The Math, even though I'm not, so maybe I'll just stop casting so as not to break the rules of The Math"?

It's basic maths... did you not pass that in elementary school or... ?
Are you able to make a post without an irrelevant ad hominem, or...?