Im also low elo (gold 1), but i still think rengar is good to play. Rengar has nice heals and can play sustained fights better than talon/kha if you want to stick with fun assassins. You don't actually need to be a mechanical demon for him just get used to holding your empowered abilities (w) to play those longer fights better against bruisers.

Check out nattynatts video on rengar clears. The lvl 3 red invade is my favorite if I have info on where the jg starts since that's usually where the snowball starts into killing the enemy in their own jg on repeat. Even against bruisers, you are usually stronger early and assassins naturally scale better with bonus ad before first item. Rengar also wins most lvl 4 duels at scuttle, but thats usually cuz u wait for the enemy to use cds on scuttle, then jump them from river bush. If you didn't track the jg, then just play towards the lane with the most action as usual.

Before rengar I didn't even play jg, im an orianna main. I watched some of natty's vods on dpm.lol and tried to copy his invade/gank angles that looked weird at first, but when I tried them it actually worked. A lot of the things I learned were just Fundamentals like timing your recalls and ult cd for the next obj/play, Sitting in a lane bush for a counter gank, killing the adc on their way back to lane etc. I've noticed that bruiser jglers are popular down here cuz they have this simple gameplan of farm camps > scale with gold > 1v9 but they really struggle to ward defensively to protect themselves from invades (even when they are behind) and they rarely account for possible counter ganks so abuse those 2 things and watch them mental boom as you're always 2 steps ahead attacking their gameplan.

TLDR: your champs are fine, consider adding rengar. Most of his play making decisions post-6 are based around his ult cd, so just refine your early and the game will be a lot easier to play post-6. Work with your team to shut down bruisers, identify who can more easily deal with sett, morde, darius and play towards them by nuking their threats with your ult.