Thats not how Merchant works, though, and I highly doubt that is going to change. Merchant will more than likely still only work on in-battle gained gold, with the added benefit in the future of also raising the in-battle gains cap. So rather than looking at 1000 vs 1250, you’d be looking at 100 vs 125, which is then added to your post battle rewards (eg., the amount shown on the PvP selection screen), the total of which is multiplied by your difficulty/armor/VIP multiplier.
Merchant isn’t relevant one way or the other, because the thing that is is buffing (in battle gains) is a small percentage of what you gain total (in battle + post battle gains). In the case of souls, there just are no post battle gains (except in the case of new challenge stars), and in battle gains are most likely either 4, 6 (necromancy without valk), 24-34 (TDS in a dragon team) or 40 (2 cast valk earning at least 12 souls/cast, usually need to clear a PvP, or TDS in a non-dragon team), depending on which troops are used. With the change to necromancy, unless there are a ton of generators added or significant baseline increases, we’d still be looking at 4, 5 (necromancy without valk), 24-34 (TDS in dragon team), 40 (2 cast valk earning 14 souls/cast, TDS in a non-dragon team), and 40+ (2 casts of valk earning 16 souls per cast - mythic/20/full 5*s and statue bonus, more than one necromancy with 2+ valk casts, 3+ casts of valk earning 11+ souls a cast, TDS shoehorned into a necromancy team). If existing generators are buffed “a little”, we might see some base 10-12s in there, but nothing near the amount you’d need to take advantage of a raised cap.
This is old information. It was later confirmed by Sirrian that the caps only raise if you have the associated merchant/necromancy trait, and confirmed by Nimhain that the numbers shown were generated before Necromancy was reduced from 50% to 25%, which is why the cap was shown as 60 and not 50. Valk will be worse at two casts unless you have maxed out magic kingdoms/mythic ascended/and magic statue bonus, but better for most people by the third cast except at super low end. In most cases, it will be a wash unless you are actively trying to farm souls, in which case single-shot valk is just worse. Meanwhile, baseline gains are still super low, and theres no other “best” option replacing valk.
Actually, there is something I haven’t seen anybody consider yet. I don’t believe it has been stated yet if the trait will continue raising overall gains by 25%, or will be changed to only affect the cap. The screenshot in question shows a 1/60 on the counter, with two missing troops on the opposing side. I assume this was probably a mockup anyway, because it should have shown at least 2 with two kills, but how would a fractional soul be represented on the counter in the first place? If Necromancy ends up doing nothing for actual gains but only raises the cap, it will end up being an even bigger hit to overall production, unless you actively loop to generate your souls. If baseline increases and more generator options are coming, this would make sense, but if the generator options don’t hit the cap, it will all be pretty much pointless.