This is exactly the kind of pre-med/med student thinking that is absolutely untrue in the real world. If you want to be a leader in a field, do extended fellowship, super-specialize, and do a ton of research. Most people, even the ones who want to be "leaders", end up not doing it because the salary is low and you train forever. Instead, you either go make the real money in private practice or stay in academics working 50-80% clinical doing easy fairly unimportant research with residents to make your clinical life cushy while still being "faculty".
So even if you go to podunk U's internal medicine program, you can still go do your extended endocrine fellowship making ~$60/year, study the hell out of diabetes or whatever, and go become academic faculty making $100k/year at big name academic center . So few people actually want to do this, that it's really not that competitive. The salary differences are so pronounced in the high income specialties between mostly research and mostly clinical practice, that it's very hard to find examples of MD or MD/PhD mostly research faculty within those specialties. At the end of the day, why train longer to make 1/3 of the income. Going to MGH residency vs community residency doesn't change any of that. Unless you can't get the fellowship you want. But still, fellowships are competitive because again... The $$$! If your goal is to be some academic leader, don't worry about the $$$.
Not all competitive specialties have good lifestyle. Competitive specialties = $$$. Money + lifestyle = most competitive. But plastic surgery doesn't exactly have a great lifestyle until you make it big in your little surgery center only doing boob jobs and lipos. Until then you're reconstructing car accident victims in the middle of the night.
At the end of the day, what's important is that you do what you like doing. Yeah, money and lifestyle are important. If you decide you like being out of the hospital a lot, there are a lot of less competitive specialties with good hours. If you decide you like a specialty for whatever reason, go do it. I never fault people for picking a specialty in part based on the money, but that said, you never know if the money is still going to be there in 10 years when you're in your private practice. Meanwhile, maybe pediatrics ends up being the big winner in Obamacare and they end up driving the Ferraris while the cardiologists cry all over SDN. Who knows. If you love them babies, go at them.