Felt a need to reply since we're Buds Pro buddies. Jokes aside, I bought them solely based off Crinacle's review (and also because of the awesome violet color!). Preface: I don't know a lot about the AST and I don't own an IEM with more than 2 drivers per side. One of the rules about IEMs is that higher driver count doesn't instantly mean better performance. Tuning is more of a factor over transducer count. Yes, TOTLs usually have many driver types and amounts, and I believe crossover plays a big role. Physically, adding a lot of drivers in one tiny space won't be as effective as buying more speakers (drivers) and adding them around the room.
In the end, it is more-so about tuning. The Buds Pro are Harman neutral and the AST looks V-shaped, fairly typical for a KZ. Try out the different signatures via EQ and see if you like it. If you trust Crinacle's rankings like I do, that would put the Buds Pro at a B+ overall. Looking at the rankings for multi-driver KZs, most of them score near the C category albeit the AST isn't in the bunch. I would suggest not going through but if the experience and knowledge (zenith) is worth the price: be my guest.