Question: If you are heavier you will be stronger wether this is by fat or by muscle I think we can all agree on that. (I'm not talking about overly fat because at that point it would probably not hold true due to health reasons)

So if you have excessive fat, will you gain more muscle because you can lift heavier then the version of yourself who has the same amount of muscle but a lot less fat? Or am I missing something here?

Scenario:

Say there is a version of me of 70kg with 10% body fat and a version of me of 80kg which has the same amount of muscle mass but higher fat percentage. 

Both training the same exercises but lifting the most I can lift in a secure way, will the fat version gain more muscle mass?

Answer: 
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> If you are heavier you will be stronger wether this is by fat or by muscle I think we can all agree on that.
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On what do you base this? Apart from very few lifts where a bit more body weight helps you, I can't see a scenario that shows having extra fat helps you lift weights.

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> Say there is a version of me of 70kg with 10% body fat and a version of me of 80kg which has the same amount of muscle mass but higher fat percentage.
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No, absolutely not. If you literally only gained fat, and no muscle what so ever, you won't be stronger. (unless your central nervous system somehow adapted in such a way that you have more control over the lift) What often happens thought, is that you have gained some fat and some muscle, making you a bit stronger.

**The reason why you often see very strong dudes have a bit more fat** is because if you want to be strong, you have to eat a lot. Eventually you get to the point where it gets harder and harder to gain muscle without gaining fat. They don't intentionally gain fat, it just happens when you get to the point of eating x-amount of calories a day.

Also, don't confuse muscle size with strength. You don't always have to lift heavy to get bigger muscles. Training to get stronger is different from training to get bigger.
It's a somewhat complex question. Let's start with your first sentence:

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> If you are heavier you will be stronger whether this is by fat or by muscle I think we can all agree on that. 
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No, I don't agree. What is true is that in martial arts and boxing lighter fighters have a disadvantage, probably even against heavier fighters who have the same absolute muscle mass. (The reason is that it is harder to make heavy people lose balance, and their greater mass gives a stronger punch, even with the same muscle.) Other sports which depend on momentum profit from body mass as well, for example shot put or discus. The reason is that a heavier body can accumulate more kinetic energy during the build-up phase to the toss when it is transferred to the object.

**But this competitiveness in a fight or ability to build momentum should not be confused with the sustained force people can generate.**

It seems irrefutable that a person with more fat but the same muscle in their body can lift *less* than a person with less fat: They have to lift their fat as well which contributes nothing to the lift; it's dead weight. You can observe that when fat people climb stairs. You can also observe that when people with more body fat try to do pull-ups.

What may contribute to the general impression that many fat people are also stronger is the added demand on their muscles. Simply getting up and around trains their muscles more than those of a lighter person, so more fat usually comes with more absolute muscle mass. Therefore a 300 pound man will often easily lift another 60 pounds — after all, that's just 20 percent of his weight. He has the muscles to cope with that (but may develop tendon and joint problems in the legs). A puny 120 pound guy of the same height may struggle to lift half his body mass because his muscles have not been trained to do that by normally moving his body. But this effect — that more fat leads automatically to more absolute muscle mass — is only strong for active people. Because fat makes exercise strenuous fat people often avoid even common physical activities like walking and stair climbing, making them too weak for their weight.

So the answer to your last question is yes: A version of yourself with the same muscle mass but more fat will start out weaker (because of the dead weight) but in the long run will profit more from the same exercises because he moves additional weight with each exercise.