It's different because Mifune actually played Musashi. He was Musashi in the Samurai Trilogy back in the 50s, one of his most famous roles. So putting his face on the game's Musashi isn't random, it's kind of the most fitting reference they could've picked.
Tupac doesn't have that. He's not playing a character he's known for, he's just in the game because of the Snoop/estate deal. One feels like honoring the role, the other feels like they just wanted a recognizable name.
The people who are saying the 2PAC thing from Stranger Than Heaven killed their hype
Are the same people who enjoyed the Onimusha: Way of the Sword demo with Miyamoto Musashi's face modeled after dead actor Toshiro Mifune
So why is it different here?