my anti-d4 prep ends up with either of these positions

While thorough, your response isn't really relevant. Both the Benoni and Old Benoni are considered suboptimal openings and, objectively speaking, both are suboptimal in the same way to the same degree according to the engine evaluation. And they are completely different openings. The goal of 1...c5 isn't necessarily to transpose into the Benoni

I do like Benoni-like structures, but I mainly play 1...c5 because it incentivizes White to play into the Benko. I suggest 1...c5 as an anti-d4 opening because it almost surely forces the unprepared opponent out of their prep and into yours whereas the modern Benoni only arises out of d4-c4.

not only are both positions surprisingly playable for black, but if you for whatever reason dont like either of them just play ng6 and continue play with moves like bc5, 0-0, d6, exd5 etc. its actually a rarely known because these positions are seen so rarely in master practice but the "mirrored queenside alekhine" positions either from the blacks knights tango move order (1.d4 nf6 2.c4 nc6) or from the mikenas 1.d4 nc6 d5 move order are actually more pleasant than the original alekhine because the c5 bishop strikes at the heart of whites kingside.

i dont know why people are being so dismissive here. ITs no different than as an alekhine player studying what happens if white goes hyper agressive with white pushes, i commend you for being thorough in learning your opening.

I don’t think you read what I said.

The 1…c5 move order doesn’t encourage white to play c4. It encourages them to play Nc3.

At which point, you can’t play a Benko.

If you want to play a Benko, you should be using Modern Benoni move order.

Old Benoni - They often play Nc3 to stop the Benoni counter play.

Modern Benoni move order - They commit to c4 so you can get into it more consistently.

The Benoni is a playable opening.

The Old Benoni move order just isn’t the ideal way of playing it anymore.

'd take black and keep trading until I have pawns and 2 rooks to their one rook. With all of those pawns I could dominate the center, nullify the knights, and give the bishops nowhere to go, trade off the queens and win the end game.

I think you should take a look at the statistically most probable moves after 1...c5, because it certainly isn't 3nc3. The most advantageous line, and by far the most likely to be played at 2000 elo, is 2d5 3c4. If 3.nc3, black has a very nice position.

2...nf6 is less forcing and leaves too many options to be considered anti-d4. Even at intermediate ratings 1...c5 is more forcing.

it is well known, that unless you intend to play 2...e5 czech benoni, the 1.c5 move order is an inferior benoni move order because white does have to play c4 and can play nc3 instead? Why? the reason being that the "hole" on c4 allows white to eventually place a knight there especially after prophylactic moves like a4 and possibly a5 to hold back the queenside space grab. the knight there is considered very annoying aiming at both the backwards d6 pawn as well as clamping the queenside.

I agree the move 1…c5 is far more forcing vs. 1…Nf6, but the problem I don’t understand is how is being more forcing helpful for Black?

You haven’t explained why it’s a good thing for Black.

Against the old benoni it's not just 3... Nc3 that white will play, but also 3... e4 > 4... Nc3. 77% of the time this is the fourth move following e4. Overall you can expect to get an Nc3 setup without c4 played about 35% of games.

Furthermore, you'll get c4 about 55% of the time from the old benoni. From the indian defense you'll get c4 on the 2nd move about 50% of the time, but you also will play a zuckertort about 25% of the time where you can then play a spielmann-indian which often leads to a pseudo-benko, really an improved benoni.

The indian defense setup deals with the london pretty well after 2... c5, it wouldn't really be worth playing these Nc3 benoni setups just to avoid the 8% of london games you're liable to face.

As much as I want these old benoni positions to be good they just aren't, I'm saddened by that but it's the reality born out by statistics, engine eval, and theory. If even one of these factors were weighing in favor of the old benoni maybe I could justify playing it, but the old benoni doesn't really appear to have anything going for it. The argument you're throwing the opponent off and getting some huge skill benefit leading to an advantage is contraindicated by the statistics, which all look very bad for black even going deep into the lines - the only exception being the benko.

Their is another line Black can play using the Old Benoni move order which some people might not know about, but I use to play it!

The line is called the Clarendon Court!

1.d4 c5 2. d5

Than Black plays the bizarre looking move 2…f5.

Theoretically, The CC line is considered slightly dubious. It can be crazy fun to play though if your opponents haven’t seen it a lot before

WHAT IS THIS?

3.Nf3! Far better than 3.d5. This virtually forces Black into an inferior line of the Nimzo-Indian known as the Zurich Variation.

Of course, you would never get to play the Mexican Defense against me. I wouldn't play 2.c4 here. While a perfectly fine move, I play 2.Bg5.

Speaking of transpositions: In the early 2000s, I was at a tournament site waiting for the event to start. Next to me were two high school chess buds who were playing this strange line I only saw a few references to but never looked at for real: 1. d4 d5 2. Bg5. They went over different lines and so on as I tried to look like I wasn't paying attention. Anyhow, of course I got one of them paired in Rd. 1. So he played d4. I wanted to go toward a QGD but knew it wouldn't happen with d5, so I played e6 first. I play the French anyhow, so whichever he plays, I'm OK with it. He played c4, I played Nf6 and he had no idea how to play the white side of the QGD we transposed into. He was lost by about move 15.