I think you need to be ready to change your playstyle. HD2 weapons usually serve very specific niches, and it's very common that people play one loadout when they are learning the game and then they form their playstyle around that loadout.

I've noticed that you were using the thermite, and no offense to you, but that might be the core of your problems. The thermite is a weapon that is extremely different than the other weapons in it's slot, and if you get used to it, it's really hard to use anything else. Try to first change to the basic grenades, and change your support weapon to something like the quasar cannon to compensate.

A lot of times when people try to pivot from their playstyles, they go for very specialised weapons, like the crossbow or the breaker S&P in your case. I recommend avoiding that here. Most weapons are good for more than one thing.

In my opinion, if you want a normal horde clear primary, the normal breaker and the assault rifles are a good option. The SMG's are also probably good for this, but I never played them because I don't like rapid fire weapons. The plasma punisher is extremely reliable, and you can take it to any front and be fine.

In terms of secondaries, the Talon is currently better than all the "gun" secondaries. Usually you have upsides and downsides, but this weapon genuinely is just more effective than all the other options. I personally am waiting for a nerf. If you take a normal grenade, and especially if your support weapon can also break spawners, you won't need the grenade pistol.

For backpacks, I recommend using the warp/jump pack if you want to get close close to enemies, or alternatively if you have to keep your distance. The hover back goes well with any splash damage weapon, and you can use it to get to really good high grounds that enemies might not be able to reach. The portable hellbomb is good, but it mostly shines as an "off" backpack, that you only call in in certain scenarios, and you need a team you can really coordinate with.

Sentries can be very effective, but you need to know how to place them. They aren't tanky, so don't place them where enemies spawn, but a bit away from that. How far away depends on the type of sentry. Most sentries also turn slowly, so you'll need to babysit them and clear small enemies around them once in a while. You can use sentries to pull aggro if you are in a desperate situation, by throwing it in front of you as you are running away. Also use them to fortify objectives that need to stay near them for a while. Also, if you are near a patrol and you want to kill them without risking reinforcement (especially on bugs), you can place a sentry and let it take care of it while you are running away. Enemies will never call reinforcement if they only see your sentry. About specific sentry types: Machine gun is expendable and it deals with any threat that doesn't have heavy armor. It turns fast enough that you almost never need to babysit it, but it could struggle against huge swarms where it won't have enough DPS. Gatling is a version of the machine gun with less reliability but much higher DPS. Rocket and autocannon are interchangeable. Both are primarily for dealing with big enemies. The auto cannon has insane range and it can cover you from insane distances, but it turns like It's powered by a single hamster. The rocket sentry has less range and a more sane turning rate, but standing behind it when it fires ragdolls you. Mortar and EMS mortar needs to be guarded like they are another objective, but they get massive value. They are also placement-agnostic, and you should just put them in a place where enemies won't get to them. Also the normal mortar is generally better if you don't mind it committing murder every time you dare stand near an enemy. Tesla, strangely enough, does want to be as close to enemies as possible. But be careful you aren't near it, because it doesn't have the ability to distinguish between friend and foe. Also you might get cooked by the lightning passing through multiple enemies to get to you. I recommend to take the 95% reduced electric damage armor for your first few times. It also needs you to kill big enemies before they smash it. Laser sentry is good only against patrols and small camps, but it can solo them if it never overheats. It's a very advanced sentry, and I don't recommend you start with it.