The 21 has that "je ne sais quoi" quality about it. Non photographers will often pick out the images from that lens, without knowing even how to spell Zeiss practically, from a mixed series and say they are extra special. They can't say why exactly, but they know these particular photos are exceptional in their rendering. The Canon's are very sharp, but they lack that je ne sais quoi quality, which is of course partly the basis for this forum.
That said, if you need tilt shift, you need it.
BTW, I recently picked up the CZ 35mm PC at less than half the price of the 24 TSE mkII. It doesn't tilt, and it isn't as wide as the Canon, but it should have the Zeissness about it. Tilt is nice, but shift is what you need for architecture and panos. You could almost pick up a used 21 plus this 35 for the cost of the Canon. Not quite, but close. The 35 is reputed to be best in class at that focal length. Hard to find the 35 at a reasonable price, though, because they are few and far between.