As a battlerager I am obviously biased towards the class, but this is one area where DM's need to adlib a bit for their players. Players aren't going to find spiked armor in the majority of written adventures, if any. They usually say something like +1 studded leather armor or +2 chain shirt or whatever. DM's need to realize this when they distribute loot and understand how restricted the class really is. That armor is essentially what and who a battlerager is.
Other barbarians have the use of different types of armor or to use unarmored defense. Battleragers have AC 14 armor with a maximum of +2 dexterity bonus, giving them AC 16 at best. You can add 2 AC with a shield, but so can the other barbarians so its a wash. As players level up, their AC is going to slowly creep up. A battlerager is still most likely going to be stuck with that same armor. Other classes have the ability to cast magical armor (Mage armor) or upgrade with non-magical armor (plate).
DMs, throw your battleragers a bone. Make an occasional piece of armor drop that is spiked armor or at least create a situation where battleragers can keep up with other characters as they level up. Trust me, while the bonus spike attack is very nice, especially early on, rolling an extra 1d4 on damage isn't going to overpower your BBEGs very often.
On a side note, I wish they made spiked armor and grappling more interesting. I'm sure many of us have read about Pwent and how he would grab ahold of an enemy and shred them to pieces. Its hard to reflect that with the 3 damage from a successful grapple.