For many years, I had wanted a 12 string (for decades actually ...yes, that long). I had played the ubiquitous Guild, Yamaha, Ovation, etc, across that long expanse, and never did I feel like one called out to me. Many sounded good, some really good, but none played well enough for me to tip me over the edge. Enter a few years ago when I met this certain Taylor 655ce. Jumbo bod and 12 lovely strings of jangly goodness. Sounded great, played amazingly. Then found an RTaylor: the only guit that was capable of prying that lovely 655 out of my hands into another's. That said, I've played other Taylor 12s since that time and, fact is, they play better than
any 12-er I have ever had my hands on, over the decades, bar none (except Martin since I had only heard of them, but never personally come across one).
OK, so let's just say the Taylor plays better than any 12-er out there (yes, IMHO, but one I think most will corroborate as neck dimensions, action, and overall playability is far easier to describe objectively than "tone"). But what about tone? Well that's where I think Taylor's GS and Jumbo bodies really shine. No slam against 12-string GA owners, but I personally think that with the add'l octave strings all adding that jangle and brilliance, you need the
bigger GS/JM bodies to balance out the tone. Again, just my tonal preference, but if you try them side by side, I think you will immediately hear the differences.
As for a 12er having as much bass as a well-built 6 stringer, well that's a tall order. The
proximity of the low E and its octave string physically prevents the low E from resonating (vibrating in its arc) as much as a lone low-E string on a 6-er that obviously has
far more area to vibrate than its 12-er counterpart. Add to this the fact that 12 string guitars are typically set up with lower string height and less neck relief (to make them easier to play given the extra tension of double the strings to fret) and you have even
less free area for 12-strings to move. So not only do 12ers not have as much bass as a good (and I emphasize
good) 6-string beast, 12ers often cant get as loud. Bang all you want on a 12er and it will simply "top out" when the strings clang against each other despite your best effort in drigving them harder. 12-string guits have their beautiful sonic place; their own voice. But asking them to do what a 6-er does better is like asking a circle to be more square: it isn't a shortcoming; it's simply a facet of their voice.
All that said, a
good 12er does a remarkable job of offering full bass response and lovely low-end balance to strong mids and sparkling highs that, in a lesser guitar, can easily overpower weak bass. So if there is a difference in bass response and overal tonal balance in 6 stringers, there is an even greater difference among 12ers ...IMHO. Hope that gives you a few things to think about

Edward