It's all about small ball. The record indicates that small ball works against nearly every team in the NBA. The Suns won 61 games in the far better conference this year even though KT lost almost a month of work (from Jan 15 to Feb 14).
The key is how the Suns use Marion. Marion at PF creates mismatches on offense because bigs cannot keep him from running backdoor plays nor keep up with him on the break. On defense, Marion is very good at playing denial and creating steals. He can play them very tight because there is little risk of the big man getting around him. The only threat is to be backed down, but quick double teams can disrupt that.
The downside of small ball is that it forces Amare to play post defense where he is vulnerable to getting into foul trouble. This a bigger problem against some opponents than others.
Part of what D'Antoni likes about small ball is that it is a "high energy" style. With the right personnle, it means pressing opponents, forcing turnovers and quick, contested shots. Against opponents who play a lot of "one on one" it is highly disruptive and forces them to play faster.
It works very well most of the time. Opponents either cut down their easy shot opportunities by slowing everything down or they get caught into a running game few can hope to win. Once teams get behind, they risk getting run off the court.
In 2004-05, the Suns won 63 games with Stephen "Hands of Stone" Hunter as the only big man off the bench. The Suns management recognized they needed to upgrade and went out to get KT. But they did not abandon the belief that speed ball works.
IMHO, the only team that requires a big lineup to stop is the Spurs. The Suns need to work on being able to use KT and Amare at the same time enough to prepare for the Spurs. But I don't expect them to go to a conventional style for most opponents.