Mirrorrorrim
Hero
Sounds like this could be solved by a wildshape beastform template that sets the AC, Temp HP, and attack and damage mods.Well, the Moon Druid can't wildshape into a Brown Bear at Level 3 or Level 5. Their ability to access higher forms doesn't come online until level 6, when they get CR2, but they are following the Druid's Wildshape restrictions until then. So at level 5, it's CR1/2 creatures. This means they probably don't bother with Brown Bear as a form at all, because you can jump from CR 1/2 to CR 2 when the Druid gets to 6th level.
But, taking your example at level 5, the likely land combat forms are Ape, Black Bear and Giant Goat. All have the same HP, 19. So the difference is 15 tmp hp or 19 ... not exactly the insanely big difference here. And since the Druid doesn't revert unless knocked unconscious, to refresh that pool of temp hp in the same combat means reverting to normal form as a bonus action, then shifting again on your next turn. I'm not seeing the problem here.
What I am seeing is that the attack bonuses on these forms are +3 and +5 ... so not great.
shrug