You're presupposing we take corporate death cult. While you can certainly do this, I'm comparing the new civic in a vacuum. What if the megacorp doesn't want to be spiritualist? Or what if they want free traders or some other civic instead? Half of my thoughts on zombies are based on the fact that they're not nearly as versatile as robots, and are only useful in certain specific builds. You can use robots in 100% of builds. Zombies pigeonholes you into pretty much exactly spiritualist death cult bio ascension megacorp, which isn't very good. Megacorps as a government type are easily the worst right now due to their bigger sprawl penalties for no major benefit (branch offices are great, but not consistently useful, and you won't have them early game. Gestalts, other megacorps, and empires that don't like you are immune.) You also can't integrate vassals as a megacorp which is a major downside.
It's a 25% penalty, not a 15% penalty. Robots can also have mass produced for 2.5 assembly, making that gap narrower. Budding is only going to be providing much benefit once you get above 20 pops, robots can be built on 0 pop colonies. Sure, you can have more zombies than you can have robots, but only on your home world. Any colonies you build won't be able to build zombies for years. And I've already stated my opinion that the civic is best not used as a starting civic because zombies really aren't that great.
Trade laws were nerfed to only give .125 unity. Trade league still having the old value is almost certainly a bug that will be patched in the release version. And a clerk giving you 3 energy, 1.5 CG, and 1.5 Unity (fixed your numbers for 3.2 clerks. They give a max of 6 trade value with thrifty and the tradition, not 10). That is still less efficient than having other pops generate equivalent resources from artisans/bureaucrats/technicians. Even taking other bonuses into account, there simply aren't enough bonuses to trade in the game to scale clerks up to match a late game technician, which even has repeatable techs to increase its output.
The only nerf to merchants was the merchant guilds +2 unity being removed, the job still gives the same amount of trade value as it gave before. And now that you don't actually need merchant guilds to make a trade federation, you can run an entire second civic on a merchant build that you didn't have room for before. Just spitballing but you could take exalted priesthood, which replaces rulers with high priests that give tons of unity to make up for the merchants no longer giving 2 unity. One high priest gives 6 unity, or 3 previous merchants. You do lose out on some trade value but it's still net positive in unity.