Every melee DPS has Bloodbath, but many of Reaper's strongest skills don't actually benefit from it (Communio is a spell, Gluttony, Unveiled Gibbot, etc, are all abilities). It has no special advantages with Bloodbath.
Arcane Circle is weaker than Riddle of Earth on Monk. The shield is only 10% of your maximum HP. The HoT is only 250 potency in total (50 potency for 15 seconds, which is 5 ticks) and it can't crit heal. Second Wind is 500 potency and CAN crit heal for reference on how weak the HoT is. The strength of Arcane Circle comes from the fact it effects the entire party which is a strong net amount of healing, it's a very weak skill in solo play but was strong enough in raids that it warranted a nerf.
Theorycrafting examples on why it's weaker if you care: The reason Riddle of Earth is stronger is because it provides 20% flat damage mitigation for up to 10 seconds with no limiting factors, unlike Arcane Circle which has a fixed shield amount of 10% of your maximum HP and a HoT that does not work immediately, so it can be entirely ineffective as overhealing if your healers already topped you off before it expired. In a real scenario, say a raid AOE occurs, and deals 60,000 damage at base (this is a reasonable amount for a savage-level raid AOE more or less). Arcane Circle would prevent ~7000 damage out of that as shield mitigation, and heal you for around 4200 HP, which is maybe 11,000 effective HP value to be loose with the numbers at maximum, and you'd take the rest of the ~49,000 damage from the AOE. This is not factoring in that the mitigation might be as low as only the 7000 HP shield if your healers healed you before the HoT could work. Riddle of Earth would fully prevent 12,000 damage instead with 48,000 damage taken because it is a flat 20% mitigation immediately, and it continues to work mitigating for the full duration so it can result in even more value. Riddle of Earth scales with the amount of damage you take, because it is a %-based mitigation, so a stronger amount of damage would result in even more value, assuming it's survivable, on top of stacking with other mitigation skills. In a worst case scenario situation where an amount of damage might even one-shot you, you have more lenience with Riddle of Earth since it is more effective on higher amounts of damage. In situations where many small amounts of damage occur that add up, Riddle of Earth is also still more effective, because it is again a 20% fixed mitigation with no stipulations, while Arcane Circle is still shackled to its max HP value shield and the requirement of the shield breaking on top of that which is another potential issue.
NIN and RPR are probably more or less equally survivable, since they both suffer the issue of some of their strongest skills not working with Bloodbath (NIN has a much higher skillspeed and auto-attack speed while it has fewer skills that benefit), but NIN has a 20% max HP shield rather than a 10% max HP shield. Shadeshift is better than Arcane Circle for personal mitigation because it's simply a stronger version of Arcane Circle that lasts much longer (20 second shield vs. 5 second), so not only does it prevent more damage but it won't fall off before it can be fully broken if you mistime it.
SAM has the worst personal mitigation of any melee DPS. It just doesn't really have anything anymore besides Third Eye and Third Eye sucks. Its Bloodbath healing is great during its burst, but it's not reliable since the rest of the rotation is relatively low potency.
DRG's just pretty terrible in terms of survivability. At least it doesn't have the lowest magic defense of any job anymore, though. Its Bloodbath healing is probably better than NIN's at least?