True, and a lot depends on the specific individual and frequency/dose being used. I mean, someone who's been sniffing 2-3 bags of ECP to get high for three to six months could w/d at work (I did it pretty comfortably with nothing but a tiny bit of clonidine (<.1mg), antihistamines (diphen, 50-100mg), IBU (600-800mg every 4-6hrs) and a tiny bit of lorazepam (0.25mg 1-2x per day for four days or just 0.5mg at night and none during the day)). Whereas, me, two years later, well I could still w/d at work (and law school for that matter), it just sucked a lot more.
But I have been friends with a few folks who use enough so that you're absolutely right, acute w/d would put them DOWN regardless of circumstances.
With the unmediated w/d of methadone though, it would still depend on the individual, dosage, etc. etc. I imagine. I have known a couple folks on higher doses who probably wouldn't be able to go to work if they went did a drastic taper, let alone c/t (e.g. wouldn't be much better than w/d off a huge dope habit, although it would last a lot longer and in that sense suck a lot more in terms of jeopardizing their employment).
Wanna hear something funny though: The best activity I have ever found to do while in w/d, especially if you can get your basic comfort meds (LOW dose or no benzos OR gabapentin/pregabalin at sub recreational levels, or really just a tiny bit of clonidine and IBU), is to spend the time one is in w/d volunteering. Just staying busy is HARD as hell in w/d, and not doing so makes it infinitely worse, for all those concerned.
Find a volunteer position at some poverty stricken school or, if you're like really looking the part of the w/d junky, just find some soup kitchen or whatever. Hell, if I hadn't had such negative experiences with them, I'd suggest going to meetings and getting a commitment or two (but I'm not going there). The fact you're kept busy plus feeling like you did something positive, at the end of the day, makes even c/t withdrawal so, so much more bearable. But, of course, you'd need a lot of comfort meds to get a hard core users into the visible condition necessary to volunteer by reading to kids in elementary school...
At the end of the day though, it's all about the individual, their habit and drug. We can (and should) generalize, but I bet we'd also all agree that that, how people experience drugs differently, is primary to any generalizes, no matter how accurate or useful, we can make.