I had Zen Blades with series parallel switches and found the same thing. Parallel had good clarity but no booty so the switches always stayed in series.
Yeah. I can't imagine a time when I'd ever want parallel mode.
I have a G&L L-2500 that has a series/parallel switch...but those MFD pickups have two banks of magnets per pickup (basically two pickups in one cover), so the series mode is VERY bassy and loud. So I run them mostly in parallel mode. The ZenBlades being a single sensing pickup only has one source of string sensing, so when you run them in parallel, you get a drop in output and low end.

