Don't raise it with the coach. That's obnoxious. ("Hey, I've noticed your athletes are all getting worse. Care to comment?") Plus you wouldn't get a useful answer from him anyway.
I would look harder at the team's history: how have the juniors and seniors done compared to high school? Feels like you need to look at the longer-term record. Also, if you really like the school, plan to take a visit and talk to the athletes about it, i.e., what's training like, what do they think of the coach, etc etc.
At the end of the day, if running is important to you -- and if you're not sacrificing academics in any significant way because, let's face it, you're not going to be a pro/olympic runner -- then there's nothing wrong with making running part of your college decision. And it may turn out that another college has a better mix of academics/running than this one does.