Linking those two things together creates a much larger playing field. Ukraine can investigate one, produce a finding on that specific thing and that’s it. Knowing that all of these people were/are in cahoots with each other and were going to profit off the whole thing, his request is one YUGE net to get all of them.
That’s a pretty legit strategy.
And, it was read somewhere (FB?) our POTUS TRUMP made the statement: “We’ve got them all. We’re draining the swamp”.
Never doubt the Man. NEVER!