There is no world in which the government should be able to force a private company to give something hugely valuable to, of all possible options, Comcast (one of the worst companies in America).
I'd rather them just block these things like they did up until the early 2000s ... but it's not unreasonable for them to break up the government granted monopoly on spectrums if they do allow mergers.
It concluded that markets with 4 or more providers were far better served (price, quality, coverage, etc) than those with 3 (which effectively is what the US will have now).
The UK blocked the merger of 3 and O2 on these grounds, as it would leave only 3 providers.