In detail I can't, not a dev obviously. It's a comparison they've made when trying to explain their design philosophy for melee combat.

If I had to guess I expect they're referring to the role that dodge, guard, parry, feint and variable strike intensity mechanics bring to interesting melee in DS1/2.

If it is a sci-fi universe, I would pretty much expect and require that ranged combat is a majority instead of melee (we are not living in the stone age, after all!).
But melee should be rewarding of course, if you can get there. Some places will probably, intentionally or not, become good for melee troops, where it is best for the ranged ones to stay back.

From the videos that I have seen, there's been a good amount of CC.
Regarding the mechanics, I am not familiar in space marine-game so I don't really know what to say about that ^^

This is a sci fi universe and there have been remarkable advances in armor desing and personal rapid transportation. A dedicated melee space marine can cover 50 meters in 3 seconds and hit you from above. The question you should really be asking is, can you survive this battlefield with just a gun.

Of course it is good to have melee help.

But that doesn't mean two armies clash together in 40k by running up all their troops and sending tactical marines to stab shoota boys and guardians against chaos space marines in melee. And definitely not against enemy CC-specialists.
They all stay back and advance when it is best suited for them.

Again though, depends on the terrain. If it is a ruins with plenty of corners, it is much easier for ranged specialists to get into close combat with each other even if they weren't trying to.