First, I do not think a non-might formation can use the overlord ability. As I interpret the rule, you can only use it to give might points to a formation or hero that already has it. Since a Mumak has no might it cannot be the receiver of might points.

Q: Can a leaderless friendly formation still benefit from the Overlord special rule even though no model in it has any Might? (p69)
A: Yes.

The FAQ says they can.

Killerkatanas - compeltely different. In those cases, the monster is a hero. Not an Epic Hero inside the monster.True

Also, if we assumed an Epic Hero COULD join a monster there are two major problems: they would replace the model (as dictated by the rules, they replace a model in the command company) for starters; secondly, there would be more Epic Heroes in the command company than rank and file troopers, which isn't allowed to happen. Also true

As for regards to rules stating that the first company in a formation is the command company, that's correct. But a monster doesn't HAVE companies, so there is no first company to BE the command company.again true

You can argue all you wish that the crew are the command company, but the rules don't state the crew are a company of any kind and there is no support for that in the book. You can houserule it and I encourage that to be the case, but in non-houserule games, you can't do it. Ever, lol. This is not true. While the mumak, logically speaking, is a monster, this is not the case. The unit entry says: "Rare formation - one company compromising a Mumak and thirteen crew". Thus, a mumak has a company, thus it has a command company, thus it can have Epic Heroes in it (up to seven, in this case).

As for why - I agree that it would be immensely useful to have Might with a Mumak. but that's also the reason why they don't have access to it. The "driver" isn't heroic in any way to warrant any Might either. A Balrog and a Dragon are hugely powerful entities which should have access to Might as they are more than mere behemoth creatures. Oliphaunts are simply large beasts, nothing spectacular in their fates or skills - they're just huge. I agree, it's silly, but it's legal. And on the other hand, you can see someone like Suladan commanding from the top of a mumak, to keep a good overview of the field.

Lastly,and this bit is to Slythar, if you know what you're doing, it's easy to charge a Mumak. Equally, if you know what you're doing, you'll avoid your Mumak getting charged. I spent a game charging a Mumak with a King's Champion to keep it out of the game and, if I lost priority, used Might to charge it. Didn't do any damage, but neither did it to the rest of my army - relatively few points tying up quite a lot.I have only once fought a mumak, and that one ran off after the nasty Uruk stuck it full of crossbow bolts, but this is undoubtedly true. I only can't see how you make sure a model with a move amount you have no influence whatsoever on doesn't get charged.

The correct way is to apply the 6 and apply the 4. Nothing says add them together...

If we do it your way, explain how you kill it outright? If you roll 6,6,3 (15+) then by my reasoning the beast is slain auto etc.

Whereas your way, the beast would only gain 2 wound counters and lost a few crew...which when you have rolled consecutive 6's...seems like a kick in the nuts tbh.