Yunru's post explained it clearly. You are now trying to shift goalposts just to be right. Rat's in the cellar were never the challenge and a PC that consistently only out DPR's a polearm master build against ray and lower AC isn't really much of a damage leader IMO.
Though there is a lost and incalculatable DPR component to GWM and that's the bonus action attack on enemy death. That actually is pretty common to cause with any 2 handed weapon in the early levels and considerably ups dpr at low levels when you have a chance of killing most enemies in 1 or 2 hits. It's actually the better part of the feat until you get to about level 3-5.
I will respond to both your posts at the same time.
So I did it my calculation based on what I can know 100%. That is the only way to put a strait answer. If your doing it scenario based, you need to out line the scenario then do that math for that. In my case, I made the scenario 100% hit rate because it is very strait forward and If I hit with all that attacks then the hit rate doesn't matter as that it is the actual out come. Now if you want to argue what ifs you have to set some qualifiers!
What's your perfect subject to attack and why? What it their HP and AC? If I am going to get a reaction why? and for the sake of comparison do then give every other ally an reaction why or why not?
You want a 4 round fight vs Hobgoblin AC18, starting 60ft away, you move first, then the Hobgoblin moves into you and ally (just so that you get a reaction with polearm master):
-------------Human Variant Fighter-------------
---Quarterstaff Versitial (1d8 + dex)
---16 Dex (1d6 + 3)
---dueling fighting style (1d6 + 5)
---Polearm master but strike (1d6 + 5)(1d4 + 5) = 16 DPR
---with Polearm master reaction attack (1d6 + 5)(1d6 + 5)(1d4 + 5) = 24.5 DPR
@ +5 "to hit" vs AC18 (40%)
Round 1: Move
Round 2: Attack with adjusted DPR 9.8
Round 3: Attack with adjusted DPR 6.4
Round 4: Attack with adjusted DPR 6.4
Total: 22.6 (or 19.2 if the hobgoblin makes you come to it by targeting another ally)
-------------Human Variant War Cleric (GWM)-------------
---Great Sword (2d6 + str)
---16 Str (2d6 + 3)
---Human Variant Feat: Great Weapon Master +10 (2d6 + 13)
---War Prist Bonus Action (2d6 + 13)(2d6 + 13)
---War Domain 1st level Spell: divine favor +1d4 (2d6 + 1d4 + 13)(2d6 + 1d4 + 13) =DPR 45
@ +0 "to hit" vs AC18 (15%)
Round 1: Move, cast divine favor
Round 2: Attack with adjusted DPR 6.75
Round 3: Attack with adjusted DPR 6.75
Round 4: Attack with adjusted DPR 6.75
Total: 20.25
-------------Human Variant War Cleric (Sentinel)-------------
---Great Sword (2d6 + str)
---16 Str (2d6 + 3)
---War Prist Bonus Action (2d6 + 3)(2d6 + 3)
---Sentinel reaction (2d6 + 3)(2d6 + 3)(2d6 + 3)
---War Domain 1st level Spell: divine favor +1d4 (2d6 + 1d4 + 3)(2d6 + 1d4 + 3)(2d6 + 1d4 + 3) =DPR 30
@ +5 "to hit" vs AC18 (40%)
Round 1: Move, cast divine favor
Round 2: Attack with adjusted DPR 12
Round 3: Attack with adjusted DPR 12
Round 4: Attack with adjusted DPR 12
Total: 36 (or 20 if the hobgoblin attacks you and not your ally)
So here it the problem with this, the great weapon master does a MINIMUM damage of 16 damage. We are listing here that it has a DPR of 6.75 however if it hits even once the HP11 hobgoblin is 100% dead, even if your fighting a thug with 32 hit points (which I believe is the highest HP below CR1 from the PHB/MM/DMG that you can expect everyone to have) their is no 2 hits that it can survive but a Human Variant Fighter, dueling fighting style, dueling fighting style with a minimum of 6 you need two hits to kill the hobgoblin and even with all 3 hits your not likely to kill the 32 HP thug with and average of 24.5 on 100% hit. If the Human Variant Fighter, dueling fighting style, dueling fighting style hits with all 3 rolls and rolls max damage it does 31 and the thug lives to the next round. If the GWM war Cleric hits twice even with minimum damage the it does 32 damage and kills the thug in the first round. This method of calculating DPR does not account for minim maximum damage limits nor does it account for the GM moving the hobgolin to an ally which means you halve to move to it and forfeit your polearm reaction which would mean the Human Variant Fighter, dueling fighting style, dueling fighting style DPR is 19.2
... which becomes so situational that it is arbitrary. It basically means you can setup an exmaple fight to make polearm master or sentinel better if we are honest about it the max damage of static 100% is the least "what if this, What if that" scenario based exercise in futility. Looking a max possible damage we eliminate the "what ifs" and get to a solid number. Is it 100% accurate? No, of course not. but in the land of what ifs there is no solid ground so I just picked the closest thing.