So far his arguments are its OP because a bunch of people here on the forum, far for being representative of the player population, say so and also because on a tourney last year it has been used 3 times.
I let you rewind the post until my first comment where I give my arguments.
I will address your first then.
(1) Originally the mechanized company had the arty barrage as a unic ability and Mr.smith couldn't remove it because the commander has been sold with the feature.
Would you agree to see the TA remove from its commander after buying it? nop, so same for the arty barrage. Fortunately or unfornately, the ability can't be removed from the doctrine unless you give in exchange something better.
(2) About the WC51 raw performance, the unit is carrying the doctrine at the moment. You're only buying the Sherman 76 because you had a good start with the jeep, Cav Riflemen are only interesting because the WC51 is there to open the path.
(3) Is it too cheap? Well it's difficult to make it more expensive than a Kubel since it lacks of combat capability before upgrade.
(4) Remove the crew? Difficult to understand the reason why, we're not talking about the pershing which is unic or Calliope/Priest where the player could abuse it to spam them.
(5) Disable its loading function once upgraded? that's not a nerf for it but for the Cav Riflemen
(6) Reduce its raw dps performing stats? I don't see them overperforming, the .50 cost 45 munitions which delay CaptBAR or LtZook, that's a clear trade off.
(7) The WC51 is still vulnerable to anything having a gun and usually disapear once a 222, a luch or HTAA hit the field. You most likely have to build a new one to use the barrage ability so adding a 200mp cost to the barrage.
I numerically labeled each of your points, and I will try to distill the arguments.
1- People purchased a commander expecting it to have certain attributes, removing those attributes takes away pieces that customers paid for, the customers have a right to have what they paid for, therefore you can't take those pieces away without giving something equivalently broken.
I do not accept this argument at all. If something is overpowered in a game it needs to be nerfed or removed regardless of if people paid for it.
2- The WC51 is the only thing that makes the commander viable.
While I do agree a couples of the abilities are underwhelming, the rest are quite decent and none are useless. That you think the WC51 is the only thing that allows the 76mm sherman to be decent is quite telling. That you didn't mention combined arms as a strength of the commander is quite telling.
3. Since the WC51 lacks a weapon stock, its cost shouldn't be increased.
I don't see how this follows. The cost of a unit should be proportional to the utility it provides regardless of if it has a weapon or not. I am not necessarily advocating for an initial cost increase, but this is a poor argument.
4. Removing the crew doesn't make sense since the WC51 isn't on the same level as the Pershing, calliope or priest.
The overall power level is irrelevant to whether a specific combination of attributes and abilities is too strong for the relative cost. If the WC51 crew makes it too survivable then its too survivable regardless of how much weaker it is in absolute terms compared to the Pershing.
5. Removing the ability to carry troops would be a big nerf to cav riflemen.
This comes down to you believing cav riflemen are not viable without the WC51, to which I disagree. Removing troop transportation upon upgrade WOULD be a slight nerf to cav riflemen, but if the whole reason you intended to use the WC51 was as a glorified school bus for CQC troops, the weapon upgrade is going to give a proportionally small increase in DPS to what you use it for.
6. Spending munitions on an early upgrade delays officer weapon timing.
It doesn't delay it too much if at all, but even if it did it doesn't matter because if the upgrade is too powerful for cost then its too powerful for cost and its worth delaying the upgrades for other units due to its cost efficiency.
7. The WC51 is squishy, and often dies once light vehicles hit the field. (this is an argument that implies the WC51 is balanced because it is squishy I assume?)
The Soviet M3 has a fuel cost, can't cap, can't self repair, has lower damage with its weapons, does not have a free engine boost, does not have an artillery barrage, does not have mark target, restricts soviets from getting AT guns/mortars/MGs until backtech, and can't be built right away. Yet the m3 also dies off around the same time as the WC51. Some, people even consider the M3, to be too strong against OKW, and if the m3 is too strong then think of how powerful the WC51 must be in comparison.
Look. I am not advocating for a specific change to the WC51, though I do have some ideas. I do however think the vehicle is overperforming and I do not think you have brought any convincing arguments against this yet.