BPB, yes they bought 170's and 190's but they got rid of the 170's and replaced them with the ATR's
They have different engines to the 190 as well, plus different everything else. At least with the 170 they had common crews with economy of scale across a bigger fleet, they had a sim and everything in place.
The 737-600 wasn't a successful aircraft, it is much too heavy and cost double what an Embraer cost. Same crews, so yes the same argument used in the para above could easily be applied to justify the 600, however on balance it didn't go that way - for a bunch of reasons.
Atlas, what makes you think the Embraer wouldn't work on resource type strips?
underslung engines yes are more susceptible to FOD but that comes down to a bunch of factors, including strip maintenance, and they have plenty of performance, but you are correct they need cash with none in sight.
Aussie FO, I am with you hoping they stick around long term.