I'm a DMC rather than an instructor, but thought I'd give my perspective as someone who's spread the course over a relatively long period.
I'm nearing the end of the course after 10 weeks - my work and family commitments mean I've had to do it bit by bit, whenever my schedule intersects with the instructors. In the meantime, though, whenever I have some time free I ring the shop and see what they have going on, just to gain experience. So, so far I've assisted on four OW courses, one AOW, one Rescue Diver, several boat dives with certified divers and a Discover SCUBA. I'm not knocking doing it quickly, I would definitely have done it all in one go if I had the time, but doing it like this, I do feel I have gained valuable 'real world' experience which will stand me in good stead when I do qualify. Plus I've had more time with the study materials, and have been able to do a number of practice skills circuits. Ironically some of the OW students from courses I assisted on will be DMs before me!
So while doing the course so slowly wasn't my preferred option, I believe it has given me more confidence than I would have if I'd done it quickly.
Bottom line, though, is that both approaches produce qualified DMs. It's up to the individual candidate and their circumstances when it comes to how much they want to put into honing their skills, and I don't think either approach is an impediment to this.
M