I’m going to play devil’s advocate here, because I think there’s a very good PvE reason for special weapons and heavy weapons being moved into the same slot. The theory behind the weapon categories in Destiny looks something like this: Your primary weapon is your standard for killing badguys. Your special weapon is more powerful, but also situational; you’re not always going to be in a position to use it. Your heavy weapon is very limited in terms of ammo, but also deals the most damage.
In practice, there were so many outliers and exceptions in what different weapons could do that those rules almost never applied. A sniper rifle has more ammo than a rocket launcher and consistently does far more damage to a raid boss, swords one-shot major enemies etc. And while those outliers are fun, they create a situation where there’s a massive range in the potential damage a player can do. That means you either balance for the players who are doing low damage and make the encounters trivial with the right gear, or balance for the players who are doing high damage and force players to bring the optimal gear to raid night, or not raid at all.
If all the most powerful weapons are moved into the same slot, then that variance in potential damage becomes significantly more manageable. I think that’s what the “freedom” line really means; not freedom to use any gun you want, but freedom to use the guns you like without feeling like you’re using the “wrong” ones.
Taking off the devil’s advocate hat, it could still be completely terrible. The kinetic and energy weapons might not be interesting enough for you to even want to use two of them, or there might still be specific weapons that trivialise encounters. Overall I’m not worrying about this change just yet, because it’s hard to judge what it means outside of the context of the entire game.