Change of mind about Reach domain: 5%.
Well, that's high for you so I'll try.
(1) Mysticism is a must for an offensive caster (as opposed to fighting with one of the Martial Domains, say, then just healing and buffing otherwise), so it's not about Mysticism vs Reach. Hard to drop Mysticism in any scenario.
(2) Increasing your reach in general is really good for offensive casters since the hardest fights get spread out all over the place, and especially for Bishop/Cleric because you want your Move actions free for the buffs.
(3) If you want to cast offensively as a Bishop/Cleric there aren't a ton of options in the first few levels (especially 2nd level), and that's where the bulk of your casts are for most of the game. Reach turns on Sound Burst as a viable spell (Close AoEs are a major pain) and turns Smite from good to great.
(4) Damage + disable spells double up your action economy, and both Burst and especially Smite get around Resists/Immunities. Smite being enemies only checks about all the boxes.
(5) Sounds like from the rest of your comments that you haven't done the math yet on how radius effects area. Even Energy Cone for instance 65/50 = 13/10 = 30% more radius, but 13^2/10^2 = 169/100 = 70% more area. The effect is substantially larger from Reach Domain.