Automail itself isn’t necessary for Al to move the suit, the soul bond was what was driving it. I could see the presence of it might have benefits for increasing his strength and provide added mass that he could use for transmutation or repairing his outer armour or creating weapons and tools using it much like Ed does when he transmutes his arm blade but largely having it would be redundant for him.

I would actually argue that he is better off without it anyway. It often gets overlooked but one of the more subtle things in fights involving Al with people who aren’t familiar with him is that Most opponents size him up and assume he is a full sized person within the armour and limited to movements and speed associated with the combined weight of both. But because he is just the suit of armour he doesn’t have the added mass, he is actually a lot lighter than one would expect and that translates into him being able to move faster, smoothly and with fine control. Ed was an exceptional at hand to hand combat, but even he admitted that Al was the superior fighter of the two. Normally armour would limit and handicap such a fighter but in Al’s case because the armour was his body he was able to use it in a way that nobody else could, turning what most people would see as a disadvantage for a regular hand to hand fighter into a significant combat advantage.