Ok, you're going to think that I'm either obstinate or dumb, but here's where I think inflating the money supply causes actual inflation. In the analogy of the score of a game, if you started giving more points for the same act, as in basketball, two points were now three pointers and three pointers were now four pointers-a single point would now be 'worth' less. So if a trip to the free throw line earned you a single point, you'd be less incentivized to get fouled and more likely to foul others.
By adding points (dollars) to the system, it decreases the worth of each dollar in the game, so all types of costs should rise against the value of a single dollar (wages, products, services...everything).
I've read your post several times and only see you mention that it wouldn't count as inflation, because the only prices would rise are those that the new wealth would buy. If the dollar itself is weaker against the whole economy, it should cause all prices to rise.
Your mention of MMT had me go to the wikipedia page for that. It's interesting, but if it says you can continually add dollars to the economy, and maintain the same value of every single dollar, they're using some new math. If on the other hand, you're saying that causing the dollar to be weaker against the economy is not inflation, but something else, then maybe I just have the wrong definition of 'inflation'.