Spacing is created by players who command defensive attention. Players with "gravity."
That can be a dangerous post player, a la Shaq, or a deadly rim-runner, a la Amare.
The easiest way for a player to create space on the floor is by being a threat to hit an open three pointer and then simply standing outside the three point line.
Spacing via shooting ability is also the easiest way to "stack" the spacing effects of multiple players.
One great post scorer creates space by attracting defensive attention down low, but if you have two of them, only one can really operate down there at a time, so the other just clogs things up.
Same story with a rim-runner, or an isolation scorer.
So long as a player is enough of a threat that the defense has to pay attention to them at all times, they can create space. But the easiest way to do it, especially in the context of a full lineup, is with three point shooters.
However, a team with only good outside shooters and nobody who is a threat to drive can still be shut down because they're being smothered on the perimeter. Just look at the Warriors toward the end of Game 7 of the 2016 Finals. Curry didn't have the legs to drive, and nobody else had the confidence or the matchup to try to take it to the rack, so they lost on a series of bricked threes.
You need to have inside and outside elements to your offense to create space. All you need is one guy who can attack open space between the three point line and the basket, though, and then you can have the rest of your offensive players drift outside to keep the lane open.
To answer the OP's essential question here, no, you can't really "space" the floor just by having quality mid-range shooters. Not in today's NBA. Opponents will pack the paint and dare you to live or die by those long twos. They will be happy to give you that shot even if you're pretty good at it.
I think the mid-range shot is best seen as a weapon for busting modern defenses by taking advantage of those shots. If you have multiple guys that can shoot 45-50% on two pointers, you can punish opponents for leaving those shots open.
Still, the math is always going to be in favor of defending the paint and the three point line and living with the results if your opponent gets hot from mid-range.