Prone needs errata/rework

If you don't like that Reach weapons have disadvantage when attacking from further away, just rework the Prone condition to work like this:

Prone

• A prone creature's only movement option is to crawl, unless it stands up and thereby ends the condition.
• The creature has disadvantage on attack rolls.
• An attack roll against the creature has advantage if the attacker is within 5 feet of the creature. Ranged attack rolls against the creature have disadvantage.

Now no more Disadvantage on your melee attacks with Reach, and the condition stays simple and easy to remember.