Re: How would the game break if one used a "single initiative" system?
 

One good thing about the RAW dynamic adjDX action order is that it creates meaningful choices. If, for instance, you have a high-DX fencer who wants to aim a shrewd thrust for higher damage, he must suffer a DX penalty that could well allow the enemy to strike first.

Re: How would the game break if one used a "single initiative" system?
 

I concur. I really don't have any problems with RAW when it comes to action order. The choices available create their own randomness in the action phase.

Re: How would the game break if one used a "single initiative" system?
 

Probably the best thing about playing TFT RAW is that you are presented with a lot of situational choices that influence outcomes pretty strongly, so there is definitely a skill to playing well. Combine that with the generally balanced power level of the game, and high degree of vulnerability everyone/thing has, and it means your success or failure depends more on you and less on some brute force advantage your character's stats or equipment might provide. A lot of the ways you might imagine changing game tend to dilute that strength, I think.