You are so close to having the pieces for a 20-second clear of spider 20.
Coldheart X2 with about 250 CDMG, 70% CR, and 170+ SPD. One CH with high ACC and lower speed than the other one
Armiger with about 250 CDMG, 100% CR, and 170+ SPD. Faster than the two CH.
Rugnor Goldgleam with high ACC and 170+ speed, but faster than the above three
Normally what you'd want to close that team out would be someone with a damage booster - something like Gurptuk or BEK. I don't see those two in your list, though. But what you might be able to do to finish it off is use an AOE HP Burn. Unfortunately, UGalek's HP Burn requires him to have an ATK buff, which you don't have from that lineup. If you don't already have him Akoth the Seared is "free" from Doom Tower normal, and he has a guaranteed HP burn on all targets. That would close out your team.
Basically - you'd open with Rugnor's DEF down and Weaken, then Armiger would hit for about 0.5-0.7M dmg, and your two Coldhearts would hit for around 1.5-2M dmg, for a combined roughly 4M damage. Spider has 5.5M HP, so that would leave her at about 70% remaining HP. Then Akoth would AOE HP Burn them all, and Spider would take a combined 11 burns from all ten spiderlings plus herself. Each burn would tick for roughly 5% of her HP, for a combined roughly 50% to finish her off.
This'll take a bit longer than the 20 seconds I quoted at the top, since you would need to wait for all ticks to complete - you're probably looking at maybe 35-40 seconds, but should still be basically a guaranteed win. The only risk is Rugnor getting resisted.