What is it like being a Military Intelligence officer branch detailed to Infantry, Armor, or Field Artillery?

I cannot answer that question - the enlisted world works differently. But I can tell you that I enlisted Infantry and then re-enlisted MI. While I have no advice for what the Officer world looks like regarding internal pokitics, I can tell you PAY ATTENTION during you combat arms time. Understanding the way the grunts think, perform, and plan will pay off remarkable dividends when you transition to your MI role supporting them. When I was fathering Intel and writing reports as a HUMINTer, I had a thorough understanding of what the grunts wanted to know, what questions to ask, and what to put up front in my reports.
Most of the top tier MI Officers I served with / under were either prior service or branch detailed. While it is true that you will be behind your "MI pure" counterparts when it comes to procedure, knowledge of assets (and how to use them), and Intel-specific language, getting that grunt experience will soon set you apart for your ability to give the combatant Commander what (s)he wants and needs.

Simple, you stay on your detailed branch as a 2LT/1LT (PL Leader, XO, etc..), then go over your branch’s CPT’s Career Course. On some instances you might request to stay on your detailed branch; not always guaranteed!

As both majors have advised, stick to you detailed Branch until you are ready to attend the Captain's Career Course, at which time you can opt to return to your parent Branch. MI is not for the weak at heart or the mentally challenged, I believe.