It's optimizing for different environments and opponents, the speed runs only have to deal with the AI not human players and take such crazy paths the AI isn't around to really mess with them so they don't have to worry about reaccelerating. In versus it's much less likely you'll be able to avoid all the other players so you need to be able to get back up to speed after being hit. A common strategy in the online vs mode is actually back running to collect better items then cashing them in rapidly to win.

This used to be true on older patches but it's not at all how top players play these days. See e.g. https://www.youtube.com/watch?v=ejt52UgnhAo for an example of the meta that prevailed for top-level versus play around the end of MK8's lifespan (Yoshi Biddybuggy Roller or Yoshi Teddybuggy Roller depending on your preferred drift style) or https://www.youtube.com/watch?v=vvrCP50Gfj4 for a breakdown of some of the latest time trial world records. At the beginning of the game's lifecycle top speed was the most important stat, but as more tricks were developed and the game's balance was adjusted, having faster and more consistent miniturbo boosts became much more important.

(Mario Kart World, which isn't covered in this article, has a more standard speed vs acceleration trade off but in that game high-max-speed (heavy) combos have even worse problems due to the way the rail grind mechanic was implemented and what seems to be an unforeseen interaction with the coin curve see e.g. https://www.youtube.com/shorts/sPyur6BkiOs)

On the other hand, if you are a casual and want to dominate 99% races you enter at people's homes, pick Toadette (with Mr. Scooty). I don't think I've lost since 2019.

Lol skill issue... Right! But that's how you choose your weights. If you're not a great driver you need to give more consideration to acceleration.

no, even in time trials it depends on the track. If top speed were the most important metric you would see the same meta build for every world record time trial, but that's not the case.

Also, miniturbo is the single most important stat in the game, not top speed

Speedruns are for playing the track solo, right?

If you're playing normally (with other people and items), even the most skilled player can't avoid getting hit by some universal items and will benefit from acceleration.

Hence, as the author notes, the balanced build with Peach being favored among competitive players.

Acceleration is pointless because of the hidden Mini Turbo stat

Adding skill is just another dimension to the calculation.