The people that say height don't matter, are just as annoying as those that say pace doesn't matter, or everything else that doesn't matter.
In top level football, everything matters. Can you get by with a player shorter than the average CB, yes you can but it puts pressure on the player to be so much better than average in other areas.
Just because we are linked to a player doesn't mean we have to dismiss legitimate concern. To downplay his height, especially in the PL seems disingenuous. This doesn't mean he's being written off but it definitely is something to be worried about.
For teams that play a high line pressing aggressively, one of the ways to get at them is to play long balls over the top. Speed and ability in the air is needed to combat that. The best team in the league at defending this way is Liverpool with VVD, Matip and Konate who all have speed and excellent aerial ability.
Martinez might be a hit in the PL but to dismiss his height seems a bit silly to me.