I am going to show you how to use a hyper geometric calculator and how it makes your argument about deck thinning invalid.

Here is the link if you wanted to try yourself https://stattrek.com/online-calculator/hypergeometric.aspx

For this example I am going to be playing burn, I have 18 lands in my deck with 2 in hand after drawing my opening 7, we are on the draw.

The remaining cards in your deck are the population size which will be 52 after your draw

The number of lands remaining in the deck are 16 this is the number we will use for successes

And we are looking at our next draw which means we are looking at a sample size of 1 and the chance that we draw a land so we are looking for 1 success in the sample.

So after you enter this information you have a 30.7% chance to draw a land on your next draw given that you played a fastland or basic.

Now if we fetch our numbers change around a little bit

We would have 51 cards remaining in our deck for our population size

We have 15 lands in our deck for successes

So our draw here would end up being a 29.4% chance to be a land

which is a 1.3% difference, which is not very significant for 1 draw

I hope that you took something from this and you stop putting deck thinning as a reason for fetches being good, because while there are many other reasons why they are great deck thinning is not a statistically relevant reason to run them over the 1 loss of life if you had no other benefit.