Did anyone manage to beat Onslaught with either 5 sonas or 5 ziggs'?

No one can , Yasuo is a must

Doubt NA has. In the 5h I had last night I could just unlock up to Captain difficulty since it took 30-45min for each mission completion to register

Almost.

For Ziggs I've found the ideal augments to be both passive augments, the ult for 5s augment, and both of the final augments. The build is just Nashors, Rageblade, Rabadons, Lich Bane, Stinger

For Sona there's two that I think work for this comp. One is full damage, maxing out every Q bonus and adding Harsh then building accordingly (can't remember, think it was Arch, RoA, Rab, Lich).

The other is maxing out the ult's uptime and building an absolute ton of mana to spam it as much as possible.

Odyssey was bugging out on me and wouldn’t let me progress past Cadet but I would think 5 Sonas should be pretty easy based on how she is in One for All. Stacking auras and her ridiculous augments should make it very doable.

The augment that makes power chord every other spell AND reduces ult cooldown by 6 seconds for a power chord seems absurdly strong. Add in that Power Chord E stuns now and I would imagine 5 even slightly coordinated Sonas can EASILY achieve complete single target stunlock. Add the AoE powerchord augment and you can easily get AoE stunlock.

It will take a longtime though.

No Ive tried all ziggs made it to kayn then.. yea. dead. Now i can't make it past the first stage because rng. Must have got lucky last time.

Do 5 sonas with cadence, rhythm, rowdy, concerto, and cascade and maybe one or two ta with clutch to be safe. You just have to get lucky with the first round spawn and the rest is easy.