It varies between classes. I was farming EC HM gear, and still had to buy about 8 BH healer boots (as an arsenal merc) for the mods I needed because the campaign gear was so badly itemized.
For everyone except pretty succesful raid groups, you'd be in full 61 mod gear (barring weapons) quicker by sucking up BH commendations than by braving EC HM.
Many raid groups STILL havent cleared EC HM, yet pretty much all non-raiding players in the 5 man pugs are sporting full 61 mods. What does that tell you?
There are many well thought out things in this game. Gear progression and gear itemization are not among them, in my opinion.
Yeah, but the problem with saying you'd be 'in full 61 mod gear" quicker via BH comms is two fold
1) doesn't say what the mods are. For Agents, nearly every black hole piece has a patron armoring....which is much worse for every spec of each AC than a 58 skill armoring.
2) black hole comms are far more accessible via raiding HM EC than they are by going non-raid routes. 1 clear gave, I think, more than 7 days of GF HMFP grinding
So running HMEC is still far, far faster than trying to gear up without raiding it: not only because campaign has far less to "fix" than black hole (for both agents and inquisitors, it's a night and day difference), but because HMEC provides better access to black hole pieces than GF or the black hole weekly. With your example of boots, you were likely getting close to 1 set per HM EC clear. Let's be conservative and say it took 3 hours per run to clear it. Through group finder, that would take, at minimum, 10 days, and doesn't factor in that people buying black hole--and only black hole--need to buy far more pieces total.
The reason you see people who haven't cleared HMEC in full 61 gear, even optimized 61 gear, is because 61 gear has been out a long damned time. Personally, I have no issue with two routes to the same gear: one harder, but quicker, one easier, but taking several times the man-hour investment in grinding.