Well, a couple things: first, ilvl is not ilvl. While it is true that 25 ilvls of the same gear is about 25% output difference, as you get closer to the ilvl cap (227), most players are replacing poor quality gear of lower item level with high quality gear of high ilvl. When I say poor vs high quality, I mean that even if these two pieces were the same ilvl, the high quality gear would perform better for your spec.
At your ilvl at this point in the expansion, you are firmly in the ‘random covenant junk’ stage of gearing, which will probably make you feel kind of irrelevant compared to a high ilvl character in high quality gear.
Second, I would push back on the notion that switching to affliction will give you immediate improvement, especially in the kind of content you seem to be doing. Affliction is a very good dps spec, but it is not a particularly good solo/world spec, performs poorly in low level M+, and is generally a more difficult spec to pull off while requiring you to split your focus between dots and optimizing your burst windows.
In contrast, demo is a good world spec, with pretty simple to pull off your burst and has more straightforward and immediate aoe options, as well as having access to more stuns. This is where I think your build is not doing you any favors: you are currently running the dogs build. This excels at sustained, consistent damage. In world content, especially as you mentioned with killing elites and rares, cooldowns become more powerful, because the time you spend running between enemies translates to free effective dps as your cooldowns tick down, but lost dps for sustained builds.
I would personally try taking at least the Grimoire: Felguard for world content, as this will give you some frontline beef and some more burst by itself and when empowered by your Demonic Tyrant. Make sure you are doing the correct combo with your Tyrant, where you summon your Grimoire: Felguard, your dreadstalkers, and at least two rounds of imps before empowering them all. (Make sure you start with 5 soul shards already banked).
Finally, make sure your conduits are correct for the content you are doing. I’m sure you have the dreadstalkers conduits for your dog build, but I would also use the Fel Commando conduit in world content - it is not recommended on any of the guides for optimizing your dps, but in world content where you are depending on your Felguard to tank for you, it can save you a lot of time healing during combat, which is a poor use of your time, and also increases your passive dps while you are dealing with controlling mobs.
Unfortunately, there is not a lot you can do to help your problem of having difficulty casting during ground effects. Warlock is a very immobile caster in general. If you want to have more options to cast while moving, I would suggest Beast Mastery hunter - you can even pretend you’re still playing warlock if you get one of those corrupted fel hounds.
In general, try to make things easier for yourself. If you’re having trouble with your rotation and casting things when you should, I would recommend installing a weakaura package designed for your spec - this guy http^s://www.luxthos.com/weakauras/warlock-weakauras-for-world-of-warcraft-shadowlands/ (Remove the carat before copying the link) has weakauras for all classes that will consolidate your important abilities into a graphic you can place wherever you find most convenient.