-Merciless did feel weird. I mean, effective and necessary for Rimuru's plan? Sure. I don't know why they bothered to show it though. Meggido was never explained, so unless it only targets malicious people, there's no reason that given a little time it'd just harvest the necessary number of souls anyway. It seems the only reason Merciless was introduced was to show how powerful it was, and to use it as collateral for an upgrade.
-The Demon scene was a little funny. All the bodies got sacrificed (as per animation) when the Demons got summoned.. so the surviving dude was obviously the dude who still had a body.
-The 3.14% was never an issue. Full resurrection was always going to happen. Rimuru now saying that 3.14% is falsely low given the current circumstance doesn't change that these guys are all going to be rezzed, and we know it.
The demon sacrifice was also weird. "Hey, these two are happy to die for you"... "Oh I'm so envious"..
1) you could have offered yourself if you're so envious.
2) it'd have been better if the demons themselves offered.
3) it's a bit weird for Rimuru to be so ready to accept the Demon's offering. Imagine if Benimaru said "Take my life". Rimuru wouldn't say "Oh, okay. Just what I needed."
-This assumes demons "dying" is permanent and not some "return to Hell until the next summon"