[Brightcolours]

Given that you are thinking about buying a 17-55 again, your comment is a little bit nitpicking. Never thought about there's a reason that superzooms - none of them AFAIK - start at 18mm? With two lenses like 8-16 or 10-24 and this 18-400 I could cover a set for lightweight travel.

 

Or in other words: It's not Tamron's fault that Canon uses smaller sensors than other APS-C candidates and therefore would benefit from shorter FL for wide-angle - and on the other side it gives you a "longer" tele equivalence. It's not Tamron's fault and Canon themselves might see reasons to not go for a 22× zoom for DSLRs. It has yet to be proven these 400 mm can be used with satisfying results.

 

Btw., a 1.5× instead of 1.6× sensor would give 18 × 1.5 = 27 ÷ 1.6 = 16.875 

And a 1.53x crop sensor?