Hardly; if the product isn't ready, it's not ready. There are many reasons why it's not ready, from engineering challenges to manufacturing issues to software bugs.
Even implying that MS is making a mistake for not rushing a timed release is insane. That's a big part of how MS shot itself in the foot with Surface RT v1. The software side wasn't ready, from firmware fixes to buggy Office preview; if it's laggy, users would often fault the hardware. One can even argue that since full Office wasn't released until January, RT should've been released then.
The business decision-making side of things was a lot more pressured with RT v1, though, because it was entering a "crowded vacuum." MS had no products competing in the populated space yet. I'm sure it was much easier to hold off on a mini now because there will be 2 releases anyway. Polish is critical in salvaging reputation.