In campaigns where combats, typically last 2-3 or even 3-4 rounds, the cost of casting Spiritual Weapon adds up quick, just for 1-2 attacks.
If you have played the Phandalin based adventures from the Starter/Essentials kit, then you will be knowledgable about short length combats.
Homebrew content, tends to run longer,( mine does at least), per encounter, though often with fewer encounters.
The GWM feat seems quite synergistic with a Warpriest Channel Divinity. At some point in their career, a cleric is either going to be out of spells, (or at the minimum spell slots for an Emergency HW or revivify), or perhaps is unable to cast Spiritual Weapon.
GWM + Healer feats, would be the best.
A Warpriest paired with an Artillerist Artificer, would excel with the Temp Hp from the protector arcane cannon. Temp HP help keep concentration checks manageable,( amongst other things).