am I right in thinking that would be worst case scenario you have shown? as with a TI the point load weight would be spread more?
There is always a worse case scenario -- With the TI weight, you might want to avoid rocky surfaces like this if possible:
On the other hand, the wheels supporting the weighted boat (see previous post above) were aired at only 2.5 psi. -- they can hold up to 4 psi. It would be a good idea to have a low pressure air gauge though with the Trax wheels to avoid the possibility of overinflation -- would be ideal if Hobie included one with the carts or wheel upgrades, since low pressure gauges are not common.
I'm not sure what you were asking in your second question. In the forward scupper position the cart takes virtually all the weight of the boat -- you can lift the boat with two fingers!
That also means there isn't much load sharing. Hope that answers it.