I've mostly tried out Falk cards and a handful from the other spheres.
I'd say that there are two cards that were made meta: Mermaid Spear is contending for the best L3 mermaid with 5* Emana and Shufas. After her vanilla counterpart, Ex Mermaid is now worst L3 mermaid for a mermaid file, but stronk in mage soldier file.
The other card is Folrart Flying Calvary. This guy is almost as good as Ex. Merc. Girl and with all the buffs he gets can deal a lot more damage than her. Not bad for 1 SP, especially if it manages to kill something.
I'm not sure what the fuss about Mercenary Nation was. I haven't modded my MN file at all after the errata, I'm not using any cards that were in the errata, and my MN file is still doing perfectly fine.
Many of the mermaid cards are better than before and in certain matchups might give you a nice edge, but overall fail at being good enough to replace the standard line-up, except for Spear who took Ex Mermaid's spot.
Gon, your Mermaid Aquamancer file might be feasible now, but it won't come anywhere near the power of Dio or Mystere.
I agree this errata changes the meta very little, but I don't think their goal was to change the meta aside from putting an end to Overdose spam and Ex Mermaid, which they seem to have been successful because PPP07 dumped the augment file and I dumped Ex Mermaid.
Also, **** Emana nerf.