As much as I didn't like the Russ signing and would've even preferred mid-Kenny for another season I would have to say Russ is definitely more mobile, or at least more effective in how he uses his mobility, than Kenny...unless Russ just completely lost it ALL this offseason. Russ has better pocket awareness and the ability to scramble to safety or the EZ rather than fleeing a clean pocket into a concussion as Kenny does.
I can't argue with the many here that support the Russ signing that Russ is a proven commodity that definitely outperformed Kenny last year and as long as he comes in hungry and humble rather than the douche nozzle he has been at his last two spots that he will likely smoke Kenny in a fair competition...and at least he is cheap.
The thing with Kenny is everyone's arguments for him are always predicated by IFs
A franchise QB or even true starting material QB doesn't require every IF in the book to be successful, they elevate other teammates despite less-than-ideal situations
As much as I personally see Russ and his past to suggest he's cancerous to a team, he does appear to be quite the upgrade on the field from what Kenny has shown...and at least he's cheap
(in best Gene Wilder voice) you said he's cheap twice, yeah I really like that one