The duration will 100% change your outcome. Zavia's lower chance of landing gets smoothed out over longer runs, but on shorter runs you may just get bad luck. Also, running CA or AA helps hugely, since you get more chances for the A1 to land poisons.
Zavia, fully booked, has 45% chance x3 on A1, and 80% x2 on A2. That means, on average, you'll get 1 poison on A1, with decent chances for two, and low chances for zero or one. For simplicity, we'll just add them up and say you will get, on average, 1.35 poisons from A1. On A2, you'll get one on average, with decent chances for two and low chances for one. Again, for simplicity, we'll just say you get 1.6 poisons from A2. Since you're turning your A3 off, your rotation will, on average, give you 1.35*2 + 1.6 = 4.3 poisons per 3 turns, on a 1:1 tune.
Kael, fully booked, has 100% on A1 and 55% on A3. Using the same logic as above, you get 2 + 2.2 = 4.2 poisons per 3 turns, on a 1:1 tune - BUT these are weak poisons, so to compare apples to apples, we'll halve that to 2.1 poisons.
tl;dr Zavia will, on average, get TWICE the number of poisons as Kael. I'd suggest you keep track of the actual results to prove it to yourself. Record a full run's worth of data a few times - every single turn - and keep track of exactly how many poisons land after each attack.
ALSO IMPORTANT - the rest of your team. Remember that there are only 10 debuff slots. If you are filling a bunch of the rest of those up with other debuffs (ATK down, DEF down, Weaken, HP burn, etc...), there is less room for poisons - and since Zavia will put more poisons on average than Kael, you run the risk of having some of Zavia's poisons "wasted". That will significantly reduce her value.