It is more like the players will do Assessment in the first and/or the second round to seize up their opponents (knowing the enemy's Weapon Skill and Insight Rank is a good thing) from behind Defense or Full Defense. When the fight actually erupts, players usually do Assessment to learn Armor TN and Wounds so that they attack the opponents they can hit and they don't waste their attacks on dying enemies. It is like an "information is power" and "knowing is half the battle" kind of deal, and it will sure introduce small breaks in the fight when everyone is busy assessing the other (especially when changing opponents and you have to do the assessing all over again).
On the other hand, a Focus action is like a compact Center Stance, but without its drawbacks. It is, like, why wouldn't you use it? Get that Focus rolling and wreck somebody's day with Feint. Negate Defense/Full Defense Stances. Get through Wound TN penalties. But yeah, just like with Center Stance, it is going to break the action only to push it into overdrive next (this can get a little rocket arena-y btw).
It sounds like the actual problem is which stances you can perform the action in rather than a problem of the actions themselves. Its very similar to the problem of Shugenja casting spells in Defense stance because their is no reason not to and they are not penalized for doing so. I suspect most of your problems would be fixed by limiting the actions to being only performed while in Center stance.
Also L5R is a very Rocket Taggy game already. A single normal attack has a good chance of taking out characters. Feint is also a very poorly designed maneuver granting far greater benefits for 2 Raises than anything else. Complaining about things while the actual flaws are with existing mechanics isn't really giving them a fair shake.