Not sure how this flappy bird look like cause there is no image of it or whatsoever, but if that kind of games takes up 70% of cpu and runs only at 35 fps then obviously you are doing something wrong here.
Crosswalk adds ~17MB to the game (which is a bit idiotic and wasteful) but it's not that bad! Bare in mind that crosswalk work only with Android 4.0 and higher. And even if some devices support 4.0+ it does not mean they are great for games.
And yeah, I'm bit concerned about current situation with exporters too. It comes and goes with waves. Unfortunately there were more bad times then good times. Looks like when everything works as it should then it lasts for a couple of months and when it breaks it takes twice longer to fix it.