Trouble with that plan is 1) Sol and McCluskey would not have been there had the meeting not taken place, and 2) if you have the meeting under those circumstances, you put Michael in direct danger, which was unacceptable.
To your underlying point, of course it was personal as well as business. If it was *strictly* business, Michael would have never offered, much less insisted, on being the triggerman, even though it was the most effective assassination plan feasible at the time.