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Very much this. If a frame has a long reach, but very low stack, and modern slacker geo (eg 68/73) and you need to run the bars high, by the time the bars are at the correct height the reach has reduced considerably. So reach, stack, ett and ht are all important IMO.
Which is what I found on an XL Stache, with its tiny head tube. On paper it fitted, but by time bars were at right height, it was way too short.
Why TT? the Reach is more accurate and any TT measurement should be ignored.