I think a really interesting test (out of sheer curiosity) would be a blind test between the FL and the Conquest HD 8x32 for people who have never used both and are unaware of their price. I say this because I think of them of very different proposals, both amazing.
I concur with what
@Conndomat says about the "more saturated" touch on the Conquest, which can make the FL look a bit washed in comparison (hey, I'm talking about a "+1500 € washed view", so take it within its intended frame of thought). In fact, I can see how some people may prefer this characteristic of the Conquest HD over the otherwise irreprochable image of the FL. The FL is very bright, very "transparent", but for some reason I find that under certain circumstances the Conquest HD might show more "pop/punch" (whatever you want to call it). I won't say the view through the FL is "lifeless", but sometimes I think the Conquest HD might be a bit more vibrant (yes, a true and genuine exercise of hair splitting going on here).
Also, the way both present their lovely view is also quite difference when it comes to edge sharpness, where the FL degrade a bit more towards the edge (as other size/magnification in the FL family do). Nothing wrong here, again, just a matter of preference, many people would hardly notice any difference if at all (while others simply concentrate on what happens on the centre of the image).
Size and bulk follow what I mention above regarding the view: both are nice to hold, very reassuring. Both have that no-nonsense utilitarian look that Zeiss used to be so good at before the very refined looking SF. But they follow different paths to achieve this nice feel on the hand. The Conquest HD are some of the heftier 8x32 I've experienced, they are on the heavy side, and they probably feel heavier (in a good sense) than they are. This can please some who find this reassurance an advantage helping them getting a steadier view. The FL has this very peculiar and slightly quirky (especially for 2023) ridged bold and stubby body that can be a bit of a pot of Marmite, you either love it or hate it. They are very light, and feel lighter, compared to the Conquest HD, due to their full-plastic construction.
And last, but not least, I think if dealing with these two you have to talk about focus wheels, because, again, both have a distinctly different approach with exceedingly good results. Focus on the 8x32 Conquest HD is really fast, buttery soft, this can be a dream come true for many birders (or a step too far for others; for example, given the shallower depth of field of 10x32, I think that it must be seriously taken into account for the 10x). The FL has a more "dry" but also technically perfect approach. I find that on the FL the wheel itself feels less solid than the Conquest HD, and because it hides the dioptre locking mechanism inside, can give a feeling of being "hollow" (so to speak). Where the focus on the Conquest can seduce some because of its speed and fluidity, the focus on the FL can seduce many with its mechanical precision. Both incredibly good, both very different.
So there you have it. If you forget about price, resale value and focus solely on the optical, mechanical and fit characteristics, it is quite a challenging decision to make, since both offer so much and do things so well but in such different ways. In the end, I think both are so good that a lot of the decision to keep one over the other would have to do with very "personal" (not so much as purely optical) preferences regarding "fit and feel". Personally, I must confess that I somehow prefer the view through the Conquest HD, its focus action, but I prefer the shorter and lighter body of the FL, and I can't forget its amazing clarity (that comes with the toll of that less perceived "punch"). It's a tough one, which only speaks highly of the 2nd tier Conquest HD, really being an "enfant terrible" on the Zeiss family and challenging the venerable grandad FL.
