|Abel's stat spread makes him flexible as either an offensive or defensive option on a Horse team. This build aims to maximize his outgoing damage with his default weapon Brave Lance+ and Death Blow 3, while tanking his defense.
With another member of the team utilizing Hone Cavalry, Abel's offensive stats are pretty good. 50 atk (56x2 damage on the charge) 33 speed. Most anything fast enough to double you is squishy enough that you can assault them to kill them. Seeing as you're on a horse, that's actually pretty easily done. He might not win as many matchups outright as Reinhardt, but there's less being run in the Arena that's a straight-up Counter to him. Between the two, Abel is a more balanced companion to a Cecelia.
Hit and Run allows Abel to retreat after he engages on an enemy. Although not as effective as fliers due to inability to move onto forest terrain, being able to attack and retreat to be Repositioned away more easily by allies is still a powerful option. Drag Back can also be used as it essentially has the same effect, just that Drag Back will pull back a surviving enemy whereas Hit and Run will not.
He doesn't have the the defensive stats to make use of Bonfire or Iceberg, so Luna gets you the most bang for your buck. Reposition is fairly standard for a horse, especially one that is only going to see combat when he initiates it.
Seeing as he benefits a lot from Hone Cavalry, it makes him the go-to pony for Fortify Cavalry therefore. You can easily run double Hone Cavalry, however. It's up to you and how you structured your team.