I personally don't like the Harrow.
He is a shittier KoSoS and barely cheaper, so I regard him as a tax for the outrider battalion which I feel are really good since it bumps up the chance of getting your AA off from 16.5% to ~28%.
The relic on the Harrow was an afterthought, could have just as easily given the GoS +1 to casting or something else entirely.
I have to actually play a few games with the sun to gauge whether it is actually worth it or not, it does have a 15'' range, but with Reiknor having 14'' move you can somewhat easily get it into range, and if you position it good it's not like the enemy can just toss it back at you without causalities on his own.
All I know is that I love the model of the Coach and want it badly, the Battalion is there just to make the Coach more meaningful I guess.
Shroudguard with KoSoS/Reiknor + Bladegheists seems better in most instances.
While Olynder only have 7 wounds, do you believe her dying turn 1-2 is a real issue?
You can guard her from spells by investing a simple artifact, do a lot of factions have ways to dump MWs onto the other side of the table without spells?