I think Riley is right.
What he's saying is that if they didn't get Shaq then quite possibly they don't get the Big Three. The Heat had never even been to the finals prior to Shaq. They had been to the ECF only once and otherwise were the type of team that made the playoffs and lost in the first round. They had 36, 25 and 42 wins the prior 3 seasons. Wade wasn't a proven winner or the superstar he was after the Finals. He was just another guy who could score a lot.
Winning that finals cemented Wade as a true Superstar which then made teaming up with him more attractive. It put the Miami Heat and South Beach out there as destination. While they had an incredibly bad season in 2007 (Wade, Marion and Shaq were all hurt), that didn't taint the lure of the Heat all that much.
So Riley is probably right. Getting Shaq started the ball rolling and thus may have been a greater "get" than even Lebron.
Except the year before they acquired Shaq they were in the ECF Semi-Finals in Wade's rookie year. They had a 22 year old Wade, 23 year old Butler, 24 year old Odom, 23 year old Haslem, and mixed in the cagey veterans Eddie Jones, Brian Grant, and Rafer Alston. Now that team wasn't immediately going to turn into a contender like bringing in Shaq did, but that team was set up to be pretty darn good for a very long time.
Obviously acquiring Shaq for Butler, Odom, Grant, a 1st, and a 2nd was a great trade for Miami and they would do that every single time, but they gave up a lot for a very short window (Shaq was basically done after just 2 years, but they made the Finals and then won the Finals). You never know what might have been had they kept the Odom/Butler/Wade/Haslem group together or what that would have meant for James/Bosh going to Miami.
This is just Riley being butt hurt by Lebron leaving.