The importance of controls cannot be understated. What worked for older games may not be the case for modern ones. The GTA Trilogy: Definitive Edition needs to improve on the clunky design from the originals. Otherwise, newer players wouldn't get into these games. These improvements are necessary.
Rockstar mentioned that the remasters will have "GTA 5-style controller layout." This includes the weapon selection wheel. Players can freely decide between different weapons. It's a seamless transition.
Perhaps the player was using the SMG against a S.W.A.T. team. Now they need the RPG to blow up a nearby helicopter. If the SMG is Weapon D, they must shift through E and F before they get to G. It wastes precious time and leaves an opening. This is very problematic if the player carries lots of weapons.