If HBO is hamstrung by lucrative deals, then it stands to think that HBO's own deal making has prevented them from usurping Netflix. To my knowledge, I haven't heard of Netflix having overtly anti-competitive behavior but I'm all ears for examples. It seems as though HBO is capable of competing, but they have to make a risky play and get out from their cable TV bubble to do so, which is no fault of Netflix.

If anything, this shows that the monolithic telecoms that have large stakes in these cable TV brands are facilitating monopolies elsewhere because likely competitors are locked into their current markets.

EDIT: to be clear, HBO's unsuccessful attempt to be level with Netflix in the streaming arena is more "don't want to" and not "can't". I wouldn't call a lack of wanting to be monopolistic. If HBO suddenly turned around and wanted to compete directly with Netflix and got boxed out by Netflix in some way, i.e. Netflix striking deals with Level 3 or similar providers to prevent HBO from getting equal treatment, then there's a strong case for them being labeled a monopoly.