Bypass is actually longer. Somewhat easier, if someone is excessively slow on difficult terrain it could be faster but I find it slower.
Technically, anytime the trail veers over to the righthand (south to north travel) of the ridge past the Strachan/St Marks col you're in the watershed. I think the additional exposure and semi-sketchy descent over David persuaded the Parks staff to ignore the extra intrusion of that section of the trail.
Please don't hate me for it, it's not my fault! If it helps, I use my powers only for good. I did a nice taping job once on some exhausted woman's nasty blisters sitting right where the David routes split. Carried her pack to the the bail-out route down to Lions bay. This was afternoon Sunday, they had started late Friday planning on being at Deeks lake by the time I saw them.
Very well done with kids. I love that trail, but it deserves a warning label for sure.