That’s not the question.
The question was - does Trump have a right to fire Comey to impede an ongoing investigation? The answer is no. Just as he doesn’t have a right to fire him for a bribe.
Your question is moot.
1. He didn't fire Mueller (but he could have). Comey want even conducting the investigation.
2. Justice was not, and could not have been obstructed by firing Comey.
3. Any and every FBI Director, at all times, can be fired by the AG or POTUS, both of whom wanted him fired. An FBI Director is never a 4th Branch of Government, or a King.
4. It seems you think you are clever with your bribe analogy, but you came up short. The bribe would be illegal for any reason. The firing is legal. Period.