There will always be an argument as to which bike is faster, more aero, lighter, better ride quality, etc. But you have to admit that there are so many great bikes out there to choose from. You really can’t go wrong with picking from the lot of P2s, P3s, P4s (eventually), Transitions, Montellos, Deans, TTXs, etc, etc, provided it’s a good fit.
Are there any terrible TT/Tri bikes out there that we should really stay away from?
It really depends on the size. Since equivalent length adjustments (say the normal 1cm progression of stem sizes) are proportionally much more influential on a smaller bike, I’d say that there are probably almost no really bad tri bikes in the fat of bell curve sizes (51 & 54). The biggest sizes of some bikes can be problematic, as those often tend to be illogical. Are you trying to make the bike for everyone over 6’5"? Or just for guys 6’4" - 6’6". Biggest sizes tend to be more problematic than smaller sizes, except for really small bikes built with 700s.
The Scott Plasmas (1 & 2) are typical of this. The XL is EXTRA large. It has almost 3.3cm more stack than the L; to contrast, the entire stack height difference in all other sizes (XS to L) is 4.4cm. So I’d describe the XL Scott as an ill-conceived bike. Unless of course it fits you, in which case it is a wonderful bike. It’s not bad, just odd.
I think, generally speaking, that is where you tend to see the biggest problems - in the geometries of the biggest sizes of bikes. But unless you are shopping that size range, you are probably okay. So my answer is really a lot more dependent on whether you are 5’8" (probably not) or 6’8" (probably so).
And of course there is the fact that the original Plasmas, while light, were about as aerodynamic as a two story house.