How would you make a 21/21 build on lvl 30? That would be crap.
It's not that bad if you wear medium armor and put 3 points into IF. Max athletics and PS. Its very convenient if you want to level past 30, as you can just keep converting attributes to skill points and flesh the build out. However when I tried it as a 2hander with Kuyak I simply felt too squishy and too low WPF so I respecced to 21/18.
I respecced from level 33 24/18 pure 2hander to level 32 same build, but with 6 riding. So I have 8 PS, 6 Athletics, and 3 IF and usually play as 2hander infantry anyways. Same stat distribution for infantry as a level 30 build like that, but with a Lamellar Vest, Plate Mittens, and 24 strength I am fast, hard hitting, and tanky enough to stomp on Battle just as easily as max IF and 4 WM.
I miss the IF, but the WPF reduction from 4 WM to none is only noticeable in heavy armor. I even tested my armor and +3 Great Sword/Long Sword with builds like 15/24, 8 WM, 170+ WPF. There is no difference in swing speed at all, just bonus damage from the athletics that is still less than more PS. Lack of HP is very noticeable, all ranged, cav, and melee gankers take off so much of your lifebar it kind of sucks.
I think 21/21 is better in heavier armor, but 24/18 is the best for medium. Wouldn't recommend those builds at level 30 without having +3 chest or gloves to crutch on though.