I'll be surprised if your dmr has a +45mm bb, if it does you must have some bloody long forks on it!
Wheelbase is such an un-important measurement when it comes to how a bike rides you can pretty much ignore it. With regards to why bikes don't ride the same, the bb height is just one aspect out of many.
For one moment lets pretend the + 45mm bb you said is correct, the chainstay length, head angle, reach will all be different. The DMR will also be heavier and is likely to have sus forks which adds more weight and a taller, slacker front end.
Long chainstays are worse for rear wheel balance, as is a short reach and tall, slack front end, that's probably why it felt worse to backhop than your mod and the Onza.