Kishimoto didn't need to say it if he SHOWED it. The fact that Kishimoto went out of his way to show that Obito was still connected to the Sharingan despite being far away when Rin was first stabbed was him showing there is a bond there. The way he explained that it's the UCHIHA BRAIN that sends signals to the Sharingan to evolve makes it clear. You don't need him to spell it out for you since he assumes you can make connections.
Obito looking at things from "Kakashi's" perspective.
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Obito the one being enraged while Kakashi is worn out, disoriented, and fainting. Obviously in no condition to evolve the Sharingan (which he CANNOT without the godly Yin affinity that comes from the Uchiha brain).
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This it the reason Kakashi didn't remember for all those years that he had access to Mangekyo all along. He was practically already knocked out during the process.
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"When an UCHIHA who has known such strong feelings comes to lose them...The anguish and despair that proceeds from experiencing such loss...causes THEIR brains to release a special kind of chakra (Yin) that affects their optic nerves..."
By simple deduction we can rule out some things and come to a conclusion on what CAN and what CANNOT work. Since Kakashi's Sharingan had a connection to Obito even from a long distance then Yin-Release affects even without a physical connection and can still trigger an evolution. What we can RULE OUT is that Kakashi evolved the Sharingan because it takes the UCHIHA brain to release that special chakra. Thus it is COMMON SENSE that Obito was the one to evolve it and Kishimoto does not need to spell it out for you.
Now for the boulder gap...It doesn't take much weight to crush a human skull but Obito's cranium is unharmed as well as portions of his lower body. Example is that both his legs are made of flesh. The boulder was not perfectly symmetrical like you mistake it to be. If his leg is unharmed and his skull was not crushed then it is obvious there were MULTIPLE uneven spots on the boulder. You actually see the boulder covers up most of his body, even the other side yet he is completely unharmed on one side which further proves the boulder had MULTIPLE indentations.
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Differences on Sharingan? Two Tomoe Obito.
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One tomoe Madara.
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And Madara claiming Obito "slipped through"
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So since your emotions are at a peak when you're about to die it might briefly activate an MS level ability. We don't know for sure but Kishimoto hinted at something through Madara's words. If that's the case, Kakashi could not do it because he does not have that level of mastery due to lower Yin-Release.
I don't know how much simpler to make things for you.
