With Destiny 2 being a looter shooter with plenty of different items to obtain, it's only natural that some of them end up falling behind in terms of performance when compared to other options. This is dictated by the fact that Bungie makes sandbox updates for the game that are aimed at fixing the main problems in terms of balance when they are released, but other issues may arise as a result. This is precisely what happened with the most recent changes made in Season of the Splicer and Season of the Lost, and while some of those were aimed at making some weapon archetypes better, they either failed to do so or they made others worse by comparison.
There are several weapon types that could use major changes delving into The Witch Queen and Season 16, and they are all options that fell out of the PvE meta for various reasons - or simply were never part of it. Currently, there are sixteen different weapon types in Destiny 2, and four of them are often overlooked because they lack stats or damage to be competitive options when it comes to high-end PvE content like Raids or Grandmaster Nightfall Strikes. Each weapon type needs different changes made to it in order to shine, and now that Bungie proved that it can better tackle buffs and nerfs that exclusively affect PvE or PvP, some changes make sense.
Pulse Rifles
Pulse rifles are in a weird spot when it comes to Destiny 2's meta, as they deal less damage than hand cannons and scout rifles, despite having overall an archetype that would ideally put them in the middle of the other two. Both hand cannons and scout rifles did receive a PvE damage buff recently, and they feel much better than they did before, which is great since it's likely that at least one of them will get an Anti-Champion mod in Season 16. However, pulse rifles were left behind by these changes, and they are now the worst of the three.
Season of the Lost was the perfect place for pulse rifles to shine because of the Unstoppable Pulse Rifle artifact mod, which could have made them meta for those players who didn't want to use Particle Deconstruction and fusion rifles. While not all Destiny 2 fusion rifles are good, they rapidly became the dominating meta option for PvE because of their dedicated mod. Pulse rifles, on the other hand, dealt too little damage to even be considered when compared to their counterpart. As such, a damage buff of at least 10% would be highly beneficial for these guns in PvE, and a bigger percentage would likely make pulse rifles great once more.
Machine Guns
Machine guns are one of those Destiny 2 weapon types that never really got to shine outside of specific niches, and their current role in PvE is more that of add-clearing. Machine guns often come with perks that increase their damage or effectiveness based on kills, such as Rampage or Dragonfly, and while it may be fun to use these weapons as tools to mow down enemy hordes, this is extremely inefficient in terms of ammo. In fact, machine guns in Destiny 2 use Heavy ammo, which is fairly rare to come by, and not something players will have great amounts of at any given moment.
Furthermore, many players are not willing to sacrifice their Power slot for add-clearing weapons, which is why the Exotic rocket launcher Eyes of Tomorrow is the underdog in the current meta. One of the most used machine guns - Xenophage - was even nerfed with the start of Season sandbox patch, and it's now become borderline unusable because of its very low rate of fire. Despite their damage increase in PvE, machine guns are still a subpar option for all content, and they need more substantial and impactful changes to see some use.
Heavy Grenade Launchers
Heavy grenade launchers are not too different from machine guns in the sense that they too suffer from the same issues with ammo economy and an add-clearing role that doesn't really fit their potential. Recently, Xur sold a god-roll grenade launcher in Destiny 2, and while the weapon was well worth grabbing, it's unlikely that it will ever be a meta option in the current state of the game. A great example comes from Season of the Splicer, which was all about grenade launchers being strong thanks to Breach and Clear. Even then, the only heavy grenade launcher that players used all the time was Anarchy.
Anarchy is not a great comparison because it is a passive damage source thanks to its mines, which means that it can virtually out-DPS any grenade launcher in the game. And yet, even after the recent nerfs Anarchy received, other heavy grenade launchers are simply not a great pick in PvE. Buffing their damage could really benefit them, especially with Witherhoard being such a great passive damage option in the Kinetic slot.
Sidearms
With the way Destiny 2's endgame PvE content works, players need all the range they can get on their weapons to stun Champions reliably and to deal enough damage to melt them as soon as possible. Most weapons have a range stat and/or a zoom perk that can increase the effective range at which that specific weapon deals damage - the lower the range, the higher the damage fall-off when shooting from afar. Thus, most sidearms are rather useless in PvE content because they tend to have very little range and also deal mediocre damage.
If combined, these two characteristics can make a gun pretty much worthless in all non-casual content. On top of that, some sidearms also happen to have a very inefficient magazine with a low bullet count, which means that players have to reload often and a single magazine may be not enough to stun a Champion or kill more than a couple of red-bar enemies. Even weapons like Rat King barely make it into niche builds, and that goes to show how desperately sidearms need buffs. There are many more valid options in Destiny 2 than sidearms, and Bungie needs to address this if it wants to keep introducing Anti-Champion Sidearm mods every Season.
Destiny 2 is available on PC, PS4, PS5, Stadia, Xbox One, and Xbox Series X/S.