The XL london road has a 57cm seat tube. It has a 59cm top tube.
If a 59cm top tube (with a 73deg seat angle) isn’t right on that style of bike for someone who is 6’4″, then I need to go back to school I guess.
57cm is, lets not forget 22.5in. And as the most important thing the seat tube has to do is hold the seat post in place, the seatpost being more than long enough to reach to the right saddle height for someone who is 6’4″.
Of course, it’s not a classic italian road sized seat tube with horizontal top tube and all that, but that’s because it wasn’t designed as such. I’ve ridden one up Cragg Vale, then across the Pennine Way and down Stoodley Pike. It was fab.
I’m 6’2″. I rode a large (54cm).