I have no idea how big is this market in the DR, but I would assume that to all of these to stay in business the market has to be growing? I don't think many loyal customers would leave their existing courier though, so the new ones would have to, at least partially, focus on new clientele?
Also, competition should bring prices down, no? Or at least improve the service, which was already evidenced in the other thread that now you can return items free of charge. Having checked carefully all our BMCargo invoices I would bet that this service was not offered by default 3 years ago...