Unfortunately, while what you said is somewhat true (I wouldnt underestimate the value of mobility for some fights) -- its still problematic thematically/mechanically because Fire is really built around Hot Streaks / wanting and embracing crit - and im not sure I like the design of having talents piss against this on such large chunks of the encounter.
I like the suggestion I posted earlier, in that a new baseline spell given to Fire Mages which basically converts crit rating to mastery rating any time a spell is cast that is a guaranteed crit, for that cast. (Like Combustion already does, but expanded and further extended to apply to: Pyromaniac, Searing Touch, Pyroclasm, Phoenix' Flames etc)