There are a few permanents that offer more doubling up of counters, as well as ones that save counters from removed creatures, but even without these, Counter Blitz is very powerful right out of the box
Protection spells, like Crypsis and Take Up the Shield, are also great with Zethi since you have to attack with them to trigger their ability
Then, at the beginning of our combat we get to make a free 1/1 Rat token that cannot block
Even with all of that, youre not playing the most threat-dense deck (Spirits plays, on average, about 8 more Creatures than Rogues does) and you dont have the instant-win button that is Shacklegeist, so the matchup becomes a bit more work than youd otherwise have to do as Spirits
In the right build, this card could easily do more work than a Blood Artist, especially because it hits all opponents