A mess of four-strength units in MP does wonders because you don't care about being left behind; if you're not aggressive towards your neighbor you run the risk of your neighbor being aggressive instead and then you won't even be left.
First off, you should care about being left behind, in a free for all setting. Unless your intention isn't to completely win the game, in which case you're already planning to lose..
With that aside, the question isn't whether or not it works, it's whether or not you feel it's too powerful in a multiplayer setting. On a 1:1 human vs human battle the holkan rush is always advantageous to the person employing it, and in certain cases can be nearly impossible to ward off. Only a few civs have a gauranteed counter (Mali, Hammurabi, other mayans...). In a multiplayer setting this type of uu isn't what id consider a fair bonus, it's more like turning the pace of the early game completely upside down and tilting it towards one players favor.
Most multiplayer starts are generally warrior(or pre-build)/worker, since it's advantageous to get your first worker out as early as possible.You can't simply worker first, since the threat of your capital being taken by another civs starting warrior is very real. It's not really advantageous to build a warrior, then start on another right away, since the best you can do is possibly force their worker to move and then you'll likely lose your warrior a few turns later to two of their warriors or an archer. With holkans you can build a 4 strength unit practically right away after your first warrior, with a bit of a pre-build on your worker before hand. A 4 strength unit at this point of the game is very hard to remove from your land, and subsequent holkans and even axeman/chariots etc. can be added later to bolster this initial attack.
Basically your only option to stop this attack is to grab bronze working and pray you can get copper in a good spot and connected before the holkan arrives. Grabbing copper as early as possible is standard in multiplayer, but you have much more leeway since normally the other player has to connect their copper as well. If you start without mining you're already far behind, and in certain conditions you may want to grab a food tech such as agriculture or AH first. With proper scouting you can have an idea how long it'll take before they have metal, but with maya near by such a thought isn't even applicable.
Also illram, rushing with warriors is always stupid. Unless you're playing someone very bad, it's going to fail. The only outcome is that youre going to be deadlocked in a long stagnant war, slowing both you and the other persons progress significantly. You may win the war eventually, but even if you do you're practically gauranteed to lose the match. In a game where you have several other opponents to deal with as well this isn't exactly a desireable goal to aim for.
