On the other hand, if the perceived expected performance between two players is so great that you fear a relatively weaker position in the hands of a stronger player, it is rational (assuming the assessment is accurate) to target down the stronger player regardless. This is for a scenario where French player is stacking diplomatic ideas and has only naval ideas or something. It doesn't sound like what will happen here, but sometimes it really is worth getting rid of a good player, because poor players are much easier to deal with when large.
It's the kind of gambit that can get you annexed by France though, who doesn't appear to be that kind of target.
This is a tunnel vision and one sided approach. It's not all bad, but it's lacking. If Wiz routinely wins or at least places well, what is the solution? Certainly you can gang up on him and the other cream of the crop players to ensure they lose, and this will probably work if executed and followed through. This doesn't really win though. It opens the game to the opportunists poised to fill the vacuum. It just scrapes the top off and leaves a new top, which might or might not include you. Far better to identify where the winner wants to go, or how they usually go, and block their ability to win. Make a deal with other powers to divide up that territory and leave him out. Peacefully divide up the new world so he can't get his foot in the door there. Partition the rest of France and wall him off the rest of the continent unless he wants to fight you all.
For Austria, for anyone, you have to make major choices with the simple goals set in your mind: what is the short term cost/benefit? How does this help and hurt long term? How does this look to others as it happens? How will this change my diplomatic position long term? In this context, it MIGHT be cost effective short term, and it probably helps diplomatically short term, but it's a long term suicide if you ask me. If you're worried about Wiz becoming too strong, the long-term answer is not to create an even stronger barrier between you, that has a far easier time expanding back into you later than trying to cross the channel. If you build up a strong France, it will want to go somewhere, and pushing east into a surrounded Austria is far easier than trying to land troops in the isles, especially when that failed disastrously once already this game!
Wiz, I see why are you such a great diplomat. I would fear you and your diplomatic tricks in a MP game

. And that's why maybe I would do the same move as Austria

.
I see this all the time in board games. Ironically, and unfortunately, it's VERY often in my experience that the best players also give out the best suggestions. The players who try to stubbornly avoid letting the winning players "trick" them inevitably always lose as a result.
I wonder what Burgundy could gain from dismantling English France and Spain. Shouldn't Burgundy be (or become later) a natural enemy of France. This alliance can't live long. If so, than killing your alliance and then betting on French-Burgundy struggle may in fact be beneficial for Austria. Outcome: everyone weekened, Austria strengthened.
Burgundy does not necessarily have to. If they lock up the channel and push east northeast (Scandi is slumping this game anyway), and France pushes down into Genoa node and the Medit, they don't directly compete. Pretty sure the last one had a Netherlands and France hugbox, yes?