counter point
have you ever watched amateurs? 3 x 3 or 4 x 2 is often not enough to establish a clear winner, especially when the skill levels are high. Sure there is a winner regardless, but you, the spectator (and I can confirm a similar feeling as a fighter) are often left with the impression of "that was a fight?")
I dont know that it needs to be 12 rounds, but I do know that attempts to "make boxing more exciting" (there have been many, from the sound to the absolutely bizarre) in the past have generally fallen flat on their faces, because the big secret it is none of these combat sports survive or dont on the merits of their technical rulesets, but actually on the marketing and audience investment. For example, I remember during there was a big push for kickboxing and muay thai, but most particular, K1, because it was "better than boxing" because it featured more techniques, and because it was faster paced. Well trying to sell muay thai in america was a doomed venture, it never caught on at all, and K1 was only marginally more successful in the US (it was mostly a european thing, which is where it really caught on). The difference between K1 and MT is K1 got the fans invested by giving the fighters personalities and lots of media coverage, the production was fantastic quality and so on.
but none of these things have ever come close to toppling boxing. Why is the UFC the only mma promotion anyone talks about today? much the same reasons. Its not about the particular sport or technicalities, its all about marketing.