Slitherine

Compared to predecessors this game play is weighted heavily toward soft/passive strategies like Encirclement, ZOC, Supply.
The constant Retreating by enemy units also make the game less impactful and a more dull game play experience, just my opinion m'kay?

Anyone know of any mods that change rules to make it more like Panzer General or PG2?

The Rules.json file can be easily changed to achieve what you're looking for. For instance, you could nerf the encirclement penalties and increase the percent of causalities required for a retreat.

The Rules.json file is broken in regards of the Mod Manager, so the answer to your question is no. This is a similar problem with other types of game files. It's been like this since the release of the Mod Manager, and a big reason why there are so few mods. The only option would be to alter your own game files. Just make sure you save a copy of the original.