I started in army helicopters (albeit active duty), and I will say it’s about the slowest way of trying to become a major airline pilot. It’ll generally be the slowest place to build time (that only a few airlines will take), you’ll still have to do almost as much time in the regionals as a straight civilian, etc. If you really want to do it, I’d focus on a fixed-wing career when able and try to get some fw ratings either before Rucker if you can, or shortly after you get back. Then get on at a regional as soon as you can and part time it in the guard. Just know the army takes some of the most fun things and somehow makes them not fun.
Maybe the guard is different so ymmv, but I wouldn’t advise anyone to join the army to fly, especially not someone whose goal is to be at a major. Also, if your goal is to get to a major, the other part of that should be to get to a major as young as possible the way seniority plays into it. Getting on at a major at 35 compared to the same major at 30 is a HUGE difference in career earnings and QOL, especially over the next 5-10 years. Good luck with the decision. I’d recommend the ANG/AFR anyday, but if army helicopters are what you want then do it. It was never really a dream of mine, more like a nightmare I got stuck in for 8 years. But it had its awesome moments amongst the misery.