4 IPs in combat can be gotten by an adept with a hard-maxed magic spending two-thirds of their power points (and that is with the revised lower cost from SR4A), a street samurai getting the restricted gear quality and spending at least 100,000 nuyen, or a mage reaching a threshold of 4 for his improved reflexes spell (and sustaining it will either incur a penalty, or require the restricted gear quality (and an outlay of 40,000 nuyen) for the requisite sustaining focus.
So, while it is a significant advantage, it is balanced in that it requires a lot of a character's finite resources to acquire. Initiative, like many other things, can be hard-maxed at character creation; this is a design feature that many people dislike, since they prefer having room for advancement, but it is what it is. There are plenty of options available for GMs who wish a lower-powered game.
Initiative passes are important, though. A lot of the combat-oriented builds that I have seen on this board tend to neglect them, as well as Edge. Generally, any combat character should have at least 2 IP, and optimally 3. Street samurai should be tough opponents. They are people who have used augmentations to make themselves superhuman combat machines.