Where did this all originate from Jumpin?

It won't happen. You're ignoring that BOTW isn't a very accessible game whilst Odyssey is. BOTW heavily panders to experienced gamers and casuals make up a lot of the gaming market, indisputably. Odyssey is more appealing to the eye on the shelf and Mario is far more iconic than Zelda. The IP power itself is prone to beat anything else on the platform.

We can already see that Odyssey has beaten BOTW on Switch in just under 3 months, where Odyssey is at 8m~ as of mid-Jan and BOTW is 6.5m~ in 10 months or so...combining Wii U sales won't do anything, the Wii U is selling under 1,000 consoles weekly and I doubt that that 1.3m~ ish figure for Wii U will increase much beyond; probably will stay like that or peak at 1.5m. So Switch + Wii U sales still don't beat Odyssey, and BOTW isn't charting higher either, which would be its chance at surpassing it.

BOTW has better legs than previous Zeldas due to all the buzz, but I guarantee that once games like Pokemon and Smash reach the platform, Mario will fare better on the charts when carrying that weight.

SMO is at 9.07mil years end and BotW is at over 8.5mil years end. They are close (2017). 

Smo will win but botw is ironically doing well. Ita just smo is killing it. When you look at things in a better light even if SMO beats BoTW because 3D mario > Zelda... BotW can possibly outsell every 3D mario game to date (excluding Smo)

You people are heavily overstating BOTW. When more games release on the Switch, its legs will fall off. Heck, can the game even beat Mario Kart 8 Deluxe? The game isn't new; still charted better than both games in the most recent European weekly without holiday season legs. BOTW has been doing better than SMO 3 weeks in a row in Japan, but this is by a few hundreds of units, so I don't think it's surpassing SMO there either.

Nope. Mario will sell more because it can appeal to a wider demographic than Zelda.

Here are the sales figures as of March 31, 2018
Super Mario Odyssey: 10.41m
Breath of the Wild: (Switch) 8.48m + (Wii U) 1.5m = 9.98m

First post has been edited to show these results.

Now we just sit back and see how long it takes for the tortoise to catch the hare.

Actually, Zelda just beat Mario this quarter, and now Zelda is only behind Mario by a little.

Maybe this is just an exception, but if this keeps up Zelda may indeed pass Mario back up eventually. Kinda funny that so many people are saying this is impossible, and now Nintendo just revealed Zelda performed better than Mario recently lol

Mario slowed down a lot in that quarter. So either Zelda needs to slow down, or Mario needs to pick it up again soon.

More games already released and Zelda’s legs still haven’t fallen off, and Zelda just outperformed Mario this quarter. Mario is slowing down and Zelda isn’t as much..so far. 

Mario already had 1.5 million units sitting on store shelves by the end of December, Zelda didn't have that. I think the last quarter was an exception.

That suggests Mario was overshipped and is even slower than expected, tho. 

It was very impressive to see BotW shipping more than Odyssey last quarter.

Go Link!