> Ranked play is nothing other than a mechanic to match you with players of equal skill at a game.
Almost all such games maintain some sort of per player rating (ELOish usually) which is separate from ranked play and often hidden. You certainly don't need to play ranked modes just to be paired with similar skill level players.
> there's no point in competitively playing a game with a low skill ceiling.
Sure, but in combination with previous comment your inference appears to be that HotS, LoL and Overwatch are low skill cap games. I'm curious what your argument for that is. Using LoL as an example the overall ELO distribution is extremely bottom heavy with a smooth taper to the top; vastly more players in lower ranks than higher despite having consistent promotion rules. A ranking for a low skill cap game would be expected to have a bunching at the top as the skill cap is quickly reached and the outcome becomes more random.
One thing these 3 games do have in common is a low barrier to entry, but I see no correlation between that and skill cap in video games or traditional sports. e.g. a very young child can start to play soccer, but that doesn't mean soccer has a low skill cap.