I've never done it, and I could be wrong, but I swear I heard dragster S2Ks launch much higher than 4K RPM, might be the reason your setup dog'd it. I think I agree with your theory.

 

I have no idea where the boosted cars are launching but guessing still pretty high and likely much higher than 4k. On my NA car, on 200TW 255 tires, I launch at 6000 rpm + on concrete and maybe a tad lower on asphalt depending on the conditions. That is to get the tires to break loose so you can smoothly get into the powerband without it falling on its face. If the tires bite when you launch, it just dogs it (And actually puts more strain on the diff most likely). So even on a boosted car, especially if you have sticky tires on it, you would likely still be launching well above 4000 rpm to get into boost and to get some slip out of the tires off the line to keep you in the powerband.

For me, any hard launching was for autox on courses that benefitted for a hard launch. I have never drag raced an S2k so take my input for what it is. I have seen at pro solos, on more modified S2ks with rcomps, people launching upwards of 7000 rpm as well.

 

I went ahead and changed settings accordingly. Now my 2 step is set at:
6000 rpm fuel cut
5500 rpm ignition cut
12000 rpm ignition retard rev (weirdly, this setting somehow swapped itself with the fuel cut setting. When I went into settings I saw fuel cut at 12000 rpm and ignition retard rev at 4000 rpm which was the same as ignition cut. I could've sworn that retard rev was at 12000 rpm before while fuel and ignition cuts were the same at 4000 rpm)

Lol, I didn't try it out yet though

 

Most ppl definitely launch above 4 grand. Regardless of stock, tuned or boosted and tuned launching at 4 grand is just too low for our power band. I'm on 240TW street Toyo Proxes T1 Sport and the tires didn't even chirp when I raced the bikes. Prior to AEM I used to rev up to about 6000 rpm and then launch which would always chirp these tires. That being said, like you I'm not a dragster and I don't drag race my S2000. Haven't even taken her to the 1/4 mile yet lol. On rare occasions I would launch off the line but otherwise I treat her like the time attack touge machine she is

I just increased my 2 step limits to give me a larger window for manually launching off the line at higher than 4000 rpm if I need to.