Overflowing Flotsam is significantly better than Rampage. Granted, Rampage isn't very strong to begin with, but hitting twice puts this into the very strong range. (OTOH, Ironclad has mass exhaust which helps rampage a bit.)

I'm not convinced that Objective Barrier is worth taking. You would have to build a deck around it by taking excessive amounts of barrier, which is wasteful as they don't overlap.

Overflowing Flotsam: For me, requiring to trigger the Odd effect makes it a bit weaker, which is why the scaling is better (6 and 10 total additional damage instead of 5 and 8), and then having it hit 2 random enemies instead of 1 target of your choice makes it stronger against single target, but weaker against multiple enemies. I was considering changing it to dealing damage only once to reduce the omnipresence of multi-hits but I'm curious what makes you feel like damage twice to random enemies is stronger than damage once to 1 enemy.

Objective Barrier: In my playtests, this card felt very strong. It's supposed to be a combo cards with Quadruple Barrier and I often ended up with 6-7 Plated Armor per Objective Barrier (the max I reached was ~20 by taking 2 Quadruple Barrier and 2 Objective Barrier in a 25-30 cards deck at Ascension 15). I feared it might be too strong, but your comment is pretty reassuring that it might be in just the right spot