Good question (and an intelligent one to boot). A bit of both I guess. The past stars certainly had their share of so called "super domestiques": Hinault, for heaven's-sake had Fignon, JF Bernard and Lemond at his disposal at one time or another, but there certainly wasn't the same focus within a team to build a phalanx of riders that could smash the opposition into oblivion a la Sky (and US Postal before them). Roche almost single-handedly won the triple in '87. In fact, his Giro win that year was done with his teammates riding AGAINST him. Lemond in 89 had nobody to support him. The so called big teams then, Panasonic and Raleigh were all about the classics and winning the Tour was secondary. I remember Millar joining Panasonic following his maillot a poids win for Peugot and he came 4th, but had virtually zero support. US Postal set the tone for every future Tour: have 4/5/6 absolute world-class riders control the peloton and then, when it's been whittled down to the last climb, send your leader away. It's dull. It's predictable. It works.
Think of 86. Hinault had just put 4 minutes into Lemond. He just had to sit still, keep his powder dry 'til Paris and the Holy Grail, the "6th" was his. But the next day he went off the front on the 1st climb, was over 10 minutes ahead on the road, but blew a gasket and was reeled in. He was headstrong, a bull, wanted to destroy from the front, on his own. It cost him dearly. But it's what made him a genuine champion. Because he didn't care if he lost dying on his sword. He called Roubaix "a bastard of a ride, a stupid ride, I'll never do it" But he did. and he won it. Because to be a true champion, winning on the cobbles was an absolute must on his palmares. And so he went out, in the French national champion's jersey (can you even imagine Froome bothering with the British equivalent?) and battered it.
The great riders, and I mean, the truly great riders, win from March to October, Nice to Lombardy, and all points in between. someone, and I don't know when, will come along, hopefully in my lifetime and say; "I want Paris Nice, I want Flanders, I want the Giro, The Tour, the Worlds, Lombardy". And Dave Brailsford won't be anywhere near it. Because it'll require risk. And I just hope it's a Frenchman. For all the reasons I alluded to earlier.