The smaller players were the ones primarily interested in this auction, allowing them to roll more coverage to rural areas with less towers.
Most of the spectrum has some build-out requirement, so no.. it wouldn't make much sense for a company to sink $20billion into it to prevent others from using it.
There's other ways to screw over owners of spectrum. Follow the history of the 700A spectrum in the US. AT&T owned most of the lower 700mhz licenses (B and C but not A: that was T-Mobile and other rural carriers). Someone got someone to issue a report saying 700A might interfere with channel 51 television broadcasters. AT&T and the vendors created a subset band called band 17 that was wholly incompatible. This essentially screwed over the other carriers and caused a multi-year delay in band 12 deployment in the US.
Article on it: http://www.fiercewireless.com/special-report/will-fcc-requir... FCC report on the topic: https://ecfsapi.fcc.gov/file/7021920804.pdf