A few observations/ideas;
Does half pressing RT still do anything? It seems to put less power than normal strokes but doesn't use the block animations like it did in 14. Is this input identical to using the RB precision shots?
RT + down on RAS does a block which has no real use - the ball often ends up just being played onto your stumps. This could be used either for a dead bat block or a leave as someone else suggested.
LT + RB could be used for Precision lofted shots e.g. lifting the ball over the slips, chipping over the infield. Currently all lofted shots seem like risky six hits/slogs.
RT + RB could be a kind of shot which angles the bat face to redirect it using the pace on the ball, or just RT on its own if RAS is flicked at a fine angle on either side.
A few other combinations are also unused, but I'm not sure what I'd assign them to;
RT + LB (another candidate for a leave?)
LB + RB
LT + RT + RB
LT + RT + LB
Also, with clicking RS to toggle advancing down the wicket, clicking LS could be used for something - perhaps to toggle 'quick single mode'? As soon as you make contact with the ball then both batsmen will quickly sprint to steal a single? Risky but may be necessary in limited overs games, or when trying to switch the strike.
For me the more variety in strokes available the better, so if we have button combinations available on the shoulder buttons, why not use them? May be easier for BA to add new strokes now with the new mo-cap facilities.