[david_c]

In standard methods, slight preference for A. As I see it, the point of A is specifically to guard against a heart raise from LHO, which happens very frequently on this auction. Distinguishing between 4- and 5-card spade suits helps opener know whether to compete over 3♥ (say).

If you have neither 4 spades nor enough support to raise partner, there is not so much urgency since your hand is more defensive. Yes it would be nice to have a call to show this type of hand, but it feels right to give a higher priority to the hands where we can anticipate having to make a difficult competitive decision later.

If we play a 1♦ opening that shows "real" length (say 1♦ = 4+ unbalanced or 5♦332) then A becomes even better since we can happily raise on 3 cards, which takes care of most of the problem hands.

Whereas, after a short/multi-way 1♣ it's much less attractive: you've lost most of your raises, which makes any minor-suit oriented hand harder to bid, and many of these are important to compete with. So there I'd go for C, or come up with some structure specifically designed for this auction.

[Cascade]

To me it seems b/ or c/ (or d/) must be superior to a/. We play b/.

a/ seems theoretically unsound in that you use the two cheapest calls to both show the same suit. This leaves no bid for hands with some useful values and without that suit and without support and without a stopper in the opponents suit. This is not just 5332 hands but many 4333 hands and 4432 with four small in the opponents suit as well as other distributions with length 5+ in the unbid suit 5431, 5422, and with standard methods (not negative free bids) six-card suits with up to 8 or 9 useful points.

The value of being able to show useful values is when the opponents preempt and partner has a distributional hand when it makes it easier for partner to judge to take another bid or bid on to game knowing that there are useful values opposite.

[hanp]

Dbl = 4+ spades, "constructive" when 6+.
2H = either 6+ spades at least invitational, or 5+ spades GF.
2S = weak with spades (about 0-6).