I have a fair amount of experience with the VIST Speedlock system. I have the Speedlock plate on a pair of VIST carving skis, and VIST TT plates on Hart Phoenix, Hart Pulse and, like you, Kastle MX 78's.
What was not clear from your post whether you have the Speedlock plates with the adjustable bindings, or the "free" system which are fixed. I will assume that it is the first, which do permit the adjustments.
My MX78's are 176cm. I was skiing them yesterday in hard-packed conditions, soft bumps and some trees. To gain a bit more control over the tips, I removed the toe and heel and moved them one hole forward. The interval is about 3/8". I did find that the ski responded more quickly with easier tip engagement. I will try moving the binding forward an other step next time I go out.
I can not say whether this would work for you as you have not shared how the ski does not meet your expectations. But moving the binding forward did seem to make the ski feel "shorter."
Here is an image of the TT plate.
If your plate has the holes, try adjusting to taste. I should also point out that this TT plate is supposed to act no stiffness to the ski, unlike the Speedlock plate which is one piece and rigid. I have that plate on a pair of VIST carvers (116/66/101) and the TT plate on the Hart Phoenix which is the same ski (different top plate - both made by Blossom in Italy from what I can gather). In the same size, these skis are quite different because of the plate.
My advice - just play with the binding placement, little increments at a time. Once you get this ski dialed in, you may feel some of the magic.