When I lift raw, breaking off the floor is more difficult. When I use to compete in single ply the lockout was more difficult. Back then though my stance was fairly wide, especially for my body type (short limbs, long torso), but not necessary toe to plate wide. I got a nice pop off the floor with the suit, which explains the reason. Now a days my sumo is more of a modified stance, but I'm mostly pulling conventional since I started getting back into lifting again.
Also keep in mind that sumo is much more technical and not as forgiving as gripping and ripping a conventional pull off the floor. Not to mention if you lack the appropriate amount of flexibility to support your stance it can hinder optimizing your leverages.