To go back to the OP, it's probable that the best times wouldn't be set by the current champions. Instead, some second raters would come to the fore due to their better response to doping, as in a free-for-all, being a strong responder would potentially be the deciding factor.
I'm lucky in that I can wear a whole range of shoes without causing issues, so I can wear both of these, but yes, they are very different: The nimbus is a neutral shoe that feels like having a bouncy pillow under each foot. I'm happy with them but they could be quite bad if you need any stability. And it's as bulky as the kayano IMO. Or by bulky do you mean stiff?
Maybe you could go with something in between, like a ravenna?
It looks like it is a delivery company problem. Either it's a one off, which can happen, or it's a regular occurrence in which case let sportsshoes sort them out.
In the meantime, they've accepted your claim, and offered to send your order again, or refund you. All you have to do is fill a form. This looks like pretty good customer service to me, or have I missed something?