Honestly I think cleric 3 is sort of overkill.
My cleric 2 characters have maxed safety zone and the hit count for safety zone attribute. It’s nearly impossible for safety zone to be broken within the 20 seconds it lasts. With cleric 2, the biggest limitation for safety zone becomes the duration rather than the hit count. Your safety zone won’t break even with someone using basic attack on it during the full 20 seconds (the default speed for basic attack is 2 hits a second, I believe).
15 Heal titles is quite overkill. With only 10 heal titles you can already heal your party effectively and have some heal squares left on the ground most of times. With heal 15 you’ll have bunch of heals lying there on the ground as a backup heal, which is nice in a way, but also makes you feel like it isn’t necessary having the skill that high.
The rest of your cleric skills won’t be used much since Cure works better with a INT build (which you probably won’t be going since you’re going monk) and deprotected zone works better with SPR build (It’s a decent skill but not worth it alone to go for a SPR build). Divine Might 5 or 10 won’t make a huge difference either but you’ll probably want to max it to 10 rather than keeping it 5 (because theres nothing better to get). I haven’t found a decent use for Guardian Saint yet.
Paladin 1 is a pretty solid class in my opinion. Restoration 5 helps a lot with healing (although you won’t need much help with that since you’re already a healing monster) and Smite is nice to use together with Double Punch so you don’t drain your stamina as fast.
And Monk 3 by itself is a great class and one of the best DPS classes the cleric tree can provide. So you can’t really go wrong with it (unless you make some really weird stat allocation).
I think the thing with Cleric 3 is that you’re giving up on nice other utilities you could have (such as having some dievdirbys buff statues, priest ressurections and buffs, bokor zombies for tanking, etc) for sheer power on healing alone. I’m not saying healing isn’t nice, but, that’s basically all you’re getting from Cleric 3 in that path. If you were an INT build with something different than Monk 3 then Cleric 3 would become more attractive since Cure 15 is pretty damn strong by itself.
So it all comes down to this point: Are you really willing to give up on all those utilities you COULD have if you weren’t Cleric 3 for sheer amount of healing? Remember all those heals won’t be useful in every situation (you won’t even use half of them while soloing).