Hard disagree. When you do that, you unbalance it.
Reach is 10'. When you pair it with Polearm Master and/or Sentinel WHICH IS INEVITABLE, you wind up with a character who can't be touched. Remember, PAM uses the weapon's reach. And for the first two benefits, so does Sentinel. So if you add Reach to a plain spear, you are now able to lock down enemies who get within 10' of you, reach enemies 10' away with a back-end strike, and hold a shield.
What you want is a long-spear, which is 2 handed, not versatile (which a spear has). That's the trade-off. You get reach but you no longer have a free hand. And more importantly, you no longer get the back-end strike. Nor would you get a bonus from the Dueling fighting style. This way, you're not creating a super tank.
Also, think of it cinematically. Specifically, watch the fight scene between Michelle Yeoh and Zhang Ziyi in "Crouching Tiger, Hidden Dragon." It is a series of fights between a variety of polearms, including, at one point, a spear. Yeoh swings the spear one-handed at Zhang, gripping it by the base of the shaft. Keep in mind that Yeoh's character is not some 3rd level fighter. She's an epic-level master who is even capable of limited flight.
The spear is 5' long. Add 2' for the length of an arm. She bends forward, using her torso and leading leg for more extension. When the spear gets swung in the widest possible arc, the maximum reach is still less than 10'. And that's in the hands of a uniquely powerful fighter.
So, from a practical standpoint, the 5' spear cannot have Reach because it won't go that far.