I was inspired by this thread
here, in which neugey claims that 3B is the most important position. Although his caveat is that it pertains to real baseball, he does implore people to change his mind. Well, here I am, and I can say that 3B isn't even in the running for top positions in OOTP. Sorry neugey.
Setup: I took the modern day Texas Rangers, and edited all of their players to a "baseline" defensive rating of 125 for their position (1 to 250 scale). This meant different things for different positions; SS needed about 143 in Range/Error/Arm/Turn DP, while 2B needed 122 in each for instance. I also edited their bench players (except catcher) to very poor fielding ratings so that they didn't interfere with the results.
The Test: I then tested positions one-by-one, first with an excellent rating (200/250), and then with a very poor rating (50/250). I wanted to see the effect on team wins when Texas had a great 1B compared to a poor 1B, etc. For catcher only I edited both the starter and backup each time, as they would have the most off-days.
Entire season simulations took too long and had wildly variable results, so I decided to just play against the Los Angeles Angels a bunch of times. 5,000 simulations each was all I had patience for. Both the Rangers and Angels are mediocre teams that had a good mix of different types of players.
The Results: The results are attached below. Note that running the simulations again can and will produce different results. There's always some variance. But I was just looking for the overall trends.
In the end the data I was most interested in was the delta between wins with a great position player and poor position player. I then boiled those results down to wins added per 162 games. It gives you a rough idea of how many wins per season you would get if you upgraded a poor fielding position player to a Gold Glove caliber one (all bats being equal).
The Rankings:
1. CF - 8.65 wins added
2. SS - 8.52 wins added
3. C - 6.22 wins added
4. 2B - 5.54 wins added
5. RF - 3.60 wins added
6. 3B - 2.56 wins added
7. 1B - 0.84 wins added
8. LF - 0.78 wins added
Conclusions: The results are somewhat, but not totally, in line with the commonly used defensive spectrum. CF and SS are pretty much tied at the top, I'm sure I could run it a few more times and they'd be interchangeable. 1B and LF don't seem to add much value with an elite defender over a poor one, so feel free to put your absolute slugs with a heavy bat here. The position I was most surprised with was RF, and I ran that test a couple more times to be sure. At least from this test it looks to be the most important corner position defensively.
Caveats: This is not a perfect test by any means, and there's definitely some caveats. For one, the same two teams playing each other is not the ideal setup, but it's all I could do with time and computer limitations.
There may be some quirks with the Angels and Rangers that skew the results -- flyball/groundball tendencies, L/R bats, pull/spray hitters -- there's tons of variables. The Angels seem to have a fairly balanced L/R bat offense, maybe other teams have an abundance of righties.
This is also only testing the 2019 MLB environment... likely in earlier eras a lot of the defensive positions would be more important and result in higher estimated wins added with an elite defender.