A week off doesn't necessarily detrain you, in fact, depending on how you train it should make you stronger! Althought I think sometimes muscularly you might be at peak I speculate it's kind of possible to "forget" a movement with too long a rest, a kind of neural detraining so reps or load might be down because of that.
I totally believe in low frequency as well as low volume being enough or sometimes even optimal for hypertrophy, maybe because I was so influenced by Mentzer and Yates starting out. Mentzer, late in his life, wrote about one of the Barbarian brothers doing a set of leg extentions once every 2 weeks and like doubling both load and reps and putting on a lot of muscle in a few weeks. I actually believe it, but only provided you go on a PED program.
Twice I very quickly recovered muscle from illness and those times I only trained once a week simply because I needed to be driven to the gym and needed some assistance. I only trained deadlifts with a couple of sets of something for the rest of my body. Everything came back to previous peak. It's amazing how little exercise I need, I definitely could maintain almost everything training just once a week. Maybe it's "all drugs"!
Paul Cartner, that asshole lol, was mentioned and he's cited a study which proved that twice weekly training for a certain muscle didn't provide any faster gains compared to once. While I think typical exercise studies might be close to worthless for us for a few reasons, it could still be true.