I completely agree that the Moon druid is OP at lower levels, but there is an easy fix that doesn't require a useless plain vanilla stat block.
A look at the fun - but overpowered- Circle of the Moon Druid, with revised Wild Shape table, and other suggestions for your 5e D&D gaming table.
www.hipstersanddragons.com
A little OT: There is one big factor (IMO) that offsets the power of wild shape (in 5E). Beasts have "side of a barn" AC. Sure, you have a bunch of extra HP, but they are depleted
very quickly due to the low AC. When I played a Moon Druid, my wild shape rarely lasted more than 2 turns in front line combat.