IR is like the most op ability. You know exactly where your enemy is, and your sniper is never going to get counter sniped
I don't disagree that on paper it's very useful but you very rarely see OKW buy the IR Halftrack let alone the Valentine. I can only speculate why it's rarely used when it looks like it would be OP. I'm guessing that most players don't have the micro attention to be watching the IR scans while managing everything else.