Everyone is recommending 3-ways for the simple reason its a tried tested and proven setup for successful SQ systems. Tweeters and mids in the kicks, midbass in the doors, fully active = the basic recipe for a winning system.
Yes, horns are possible, and I considered suggesting them earlier in the thread, but horns come with their own complexities I felt the OP wouldn't want to tackle. Not only do horns require the right dash type/shape to fit them in, or extensive modification of a non-conforming dash, but if you really want to get down to the nitty gritty of a 'worlds final SQ competition' horn system, it is going to require its own personal tuning (such as placing acoustical foam in various places in the mouth of the horn to alter dispersion) specific to the install that would require someone with quite a bit of experience.
Even horn systems benefit from a 3-way setup. Its true that these days a handful of mids are capable of playing 80hz-1khz+ effectively, so that a 2-way horn stage is possible, but possible does not mean ideal. Ideally, you have independent control over midbass versus midrange. In my experience, and many others Ive talked to, 9 times out of 10 you actually benefit from switching the polarity of the passenger-side midbass speaker. But the midrange should not have different polarities. If one speaker does both midrange and midbass, you cannot reverse polarity on the midbass alone, and LFE will suffer. There other minor reasons that, imo, dedicated midbass setups will always be superior to a 2-way setup, but polarity control is the biggest one.