I don't understand why this bothers people so much.
In every decent brawler, there's generally a move that is best to use on a certain enemy type. Guaca just makes it into part of the strategy.
After you do the move, the shield breaks, and you can totally combo the enemey as you want. It's simply a "mash attack to win!" deterrent, nothing more.
The shield colors coincide with the color of the moves special effects too. It's a pretty intuitive thing once you get used to it, and with all the roll and jump cancels in Guaca, the only time it should REALLY be an issue, if if one starts to hammer away at moves, rather than setting up the right moves for more complex, less mashy situations.