Sacrosanct
Legend
No it is not always in the same round, given that fighters typically have higher dexterity than Clerics, more often than not the spell will not complete until the second round, because the Cleric will start it after the Fighter's turn and the fighter will complete it in round 2 ... assuming they stayed inside 30 feet for two full rounds.
Even when the Cleric goes first and it is one round it will be uncommon that they are right next to each other where there will not be a gap.
This is complete guesswork. You're just making assumption after assumption that isn't necessarily true.
Are we bumping the AOE or allowing the Fighter to concentrate on something else? Increasing the AOE on spirit guardians or letting the EK concentrate on SG so the Cleric can cast something else in the second round is rarely going to be better than the EK attacking. Not never better, but rarely better.
rarely? Show the math. I already explained how expanding a radius, even by 10 feet, is going to have a big difference. I don't know how many extra creatures it will impact because that's situational, but you would normally only do SG in the first place when you're surrounded by enemies.
Doing 3d8 extra damage each round to 6 additional creatures is greater than one round of two attacks at 1d8+5 damage. It seems like it doesn't take much to make using your action for one round to augment SG for multiple rounds the lesser of the two things.
No it is only 1-2 rounds after you get it turned on. Average combat is generally about 3 rounds, less at high levels.
Citation?
No usually. Increasing the AOE does require a slot and Tasha's Hideous Laughter or Command is going to be worth more than those 51 squares usually.
Only if you're attacking a single creature. When you wouldn't do SG anyway. A single target spell is not usually going to be better than hitting all or most targets.
Heck with Command you can actually force the enemy into that AOE!