There isn't much flexibilty in terms of team comps with what you have now for your hard lineups, mostly because a lot of them fill the same jobs and suffer from the same weaknesses. Going based on this list alone (since it seems like the champions you actually want to play), here are my recommendations:
Top: Shift Lissandra in for Darius. Darius and Garen fill the same role of off-damage tank with an execution ult. The biggest different being that Darius specializes more in damage while Garen is more sustain. Not that Darius is bad (you can leave him there if you want and add Liss), but Lissandra fills a lot of the gaps in this role. Strong AP damage, Anti-Ranged Top laner, Hard CC and reliable gap closer, flexibility in build path (can build tanky and still do damage, or go more damage oriented and still be a threat)
Mid: Regardless of how well you do/don't play Ekko, he's a relatively new champ going through his immediate post-release balance phase, meaning he's a bit unreliable (ex they shift his intended playstyle, kit, numbers to something unfavorable leaving you without much time to adjust). That being said, you should have more than just Malz as a reliable pick (who is a really good one imo). Shift in Zed or at least one AD mid laner for when your team leans towards being AP heavy. Go ahead and pop Lissandra in here too, since you're already learning her top. Also, it's nice to have an AP with a strong escape in their kit in a lane with 8 entry points.
ADC: Pick up a hyper carry, or at least someone with hard late-game scaling. Arguably Varus fits this, but he's in a rough spot making him a low tier pick as a result. Vayne, Ashe, Twitch, someone that can fit into late-game oriented comps. Shift in Caitlyn as well. Safe pick, long range making her an ideal poke champ, relevant at all stages despite not being a hyper-carry, most forgiving ADC in terms of positioning (save maybe Ezreal blink but against range, net, and trap this is debatable), no serious counter despite unfavorable matchups.
Support: No comment on Ekko support. Pick up and shift in a sustain support and a poke oriented support. Soraka is easy to pickup, Sona is an alternative to sustain. Janna is a great poke, engage, disengage, and short trade winner. Morg is a poke champ with strong all-in potential (which seems to be what you like to do, my god can you say ham pool)
Jungle: Wukong has taken quite a few indirect nerfs in the form of jungle changes, and Amumu has never had a strong Pre-6. Shift in Vi or pick up someone who does. I'm going to go ahead and say shift in Nautilus or Sejuani as well. Not both, but one or the other. They're both CC monsters, though Nautilus won't see bans nearly as much after support Naut dies down and Sej is in the process of having her kit nerfed (over the span of a few patches now)
Overall, not a bad selection, just need to patch up those holes and you're set.
or bust.
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