I’ve had more than my fair share of linguistic action (hehe) living in both Beijing and the NE, so I’m gonna be sacrilegious and take the sacred cow by the teats on this one, so to speak
“Clear” is obviously a relative concept. I can see how the eryin might make speech sound “unclear” to people exposed mainly to Southern Chinese pronunciations (eryin is also used in Dongbeihua, although less so than in Beijinghua). But here’s two specimens of the melodious Beijing pronunciation, the last emp Pooy and the writer Lao She… old enough 4 ya?
Having had intimate relations (hehe) with countless middle-aged and elderly Beijingers, they sound much like this. Not identical to “standard mandarin”, to be sure, but pretty close.
You’re correct that in the past a number of well boyinyuan (e.g. Xia Qingwho who announced the death of Mao) were from the NE. Nevertheless, most middle-aged and elderly people from the NE do not speak with a “standard Mandarin” pronunciation but with a distinctive dongbeihua pronunciation. It diverges from standard Putonghua at least as much as the Beijing dialect does. Specimens provided on demand