Defy vs TCR is as much about what I like the look and feel of as it is fit. I must confess to not having ridden either yet but the numbers suggest both should ride well.
The Defy has slightly longer chainstays and wheelbase, with the TCR being closer to my CAAD12 - I suspect the handling of the TCR would make it right for me, that’s what I like most about the CAAD12, but until try have no idea how much I will feel it.
By my reckoning TCR and Defy are the same fit in a size 54 (bear with me!)
A Defy frame (in a 54) has 22mm more stack and 5mm less reach than a TCR, for the same position (i.e. taking out 20mm of spacers) you then gain a tiny bit of horizontal reach due to head tube angle - so effectively the position is near as damn it the same.
I’ll have to see if the Defy head tube is ok or too tall as a starting point first of all, then ride them back to back. Both seem to take 32mm tyres albeit the Defy comes with less ‘racey’ wider rubber which will immediately impact the feel.
We all know less spacers ‘looks cooler’ so that will be a factor - a Defy with slammed stem versus a TCR with 20mm might influence me.
Colourway on budget is important as Giant choose some interesting colours. I’d have to love the look to buy it, even if meant I build up from a frame (flip paint) rather than off the shelf. With my likely budget (maybe next year) I will not be able to get the spec I want, so building up may be an option - cheaper wheels then upgrade later.
I used to have a Defy, the old aluminium rim brake model, and apart from buying an ‘M/L’ when I should have bought a ‘M’ it was the easiest bike I have ever owned. Great build quality, albeit with some cost saving elements, but rode well and for the money was a fantastic buy. The new Defy is very different bike but based on ownership and generally what I read I am comfortable buying a Giant bike, whether a Defy or a TCR.
Last factor is the Giant support network. I would buy from a well known local(ish) dealer who is financial stable, a friend works for, and who do everything they can to make customers happy.
Sorry have blabbed on, but that’s where my head it at on the bikes, and it is all theory till ride one.
RE adaptors - I can’t see you losing watts but you have unsupported lengths of the crank spindle sitting outboard of the bearings. The spacers sit on the shaft and are relatively loosely held by the 40nm and wave washer (spaced to 1mm). I can’t quantify or measure it, but just the principle of it annoys me and I cannot see how it does not increase bearing wear.
If the bearing shell itself is not to spec (within tolerance on diameter and aligned horizontally and vertically) going wider with unsupported lengths of spindle can only exacerbate any issue.
I sound a bit Hambini like perhaps, but versus how the Cannondale crankset fit it looks close to a bodge.
Incidentally Hambini was unusually quite complementary about a Cannondale frame recently, albeit said the BB was out of spec. I watch his videos somewhat appalled at the language and with my sensible logically head on, but cannot argue with some of the basic engineering put forward.
** This video is full of swearing, the bit you want is 16:30 in where he summarises the issue but before that he explains what the issue does***