I wound wager the exploding battery was a much bigger mainstream story than bootloops. Airlines were banning the phone.
But this is getting away from the point. I don't think bootloop problems are why LG isn't making headway. On websites and in store, all marketing is geared towards Sammy and telling you everything else is a loser.
I think the boot loops may hurt in the "geek" market, and it's hard for a phone to break through into the mainstream without first getting a sizable base in the geek market, as we are the ones that will recommend phones to our families and friends.
Remember Samsung got as big as it is by including just about every feature a geek could want back in the day, and then followed that up with great advertising to really latch on to the mainstream.