One-tricking Riven to Improve Mechanics, good or bad idea?

As someone who's a one-trick with Varus, there are some things you can learn with one-tricking.

Firstly is you learn your champion inside and out as you constantly play it. You develop an intimate knowledge your champions strengths & weaknesses and over time learn to get over these weaknesses and using their strengths to their maximum potential. This is fine if you always get an opportunity to play your one-tricked champ as you'll learn how to fight in almost every possible match up and team composition.

However there are several downsides. The biggest being that you're limiting your champion pool. Severely. Another one is your champion can be crossed off instantly if it's banned. Each champion is also unique and has a different learning strategy. If for example, your one-trick is banned and you have to select another, you won't have as much knowledge of the champion compared to your one trick.

What you do is up to you. I'm just giving you some ups and downs of one-tricking as I myself also one-trick.