You going to ignore the fact that WP barrage -DOES NOT KILL- while incendiary DO?
You going to ignore the fact that delayed fuse is completely ineffective against infantry, unless you're blisfully unaware to what the timer on the ground that appeared suddenly is and its sole purpose is to poke at static structures?
WP is a better force multiplier. hitting a crew weapon or garrison allows you to close and beat up the unit while flame DOES do damage it can actually be completely negated by moving, WP still blocks vision for half the price.
Also if you are using delayed fuse against infantry you are using it VERY wrong. Pop it on an okw truck if you want to see what it's really good for.
USF version of the MHT Is absolutely superior to the ost version. It's got more versatility as well as recrew. It should have its costs adjusted upwards slightly, but nothing too extreme.
Edit: compare WP cost to something like a molotov or normal smoke nade if you feel it's not overperforming for cost.