I wouldn't say I have the best ideas on what sort of balancing should be done.
I just have some ideas. The armies we had some longer term balance to refer back to to use as a frame of reference and then general observations that certain units were way too cheap, way too powerful, etc. I could cheat a bit, so to speak on what advice to offer. Balance for policies is different because combat wasn't changed as much as say, trade or diplomacy/tourism.
What I think is clear is where it isn't working as well, where there's overpowering or underwhelming effects. And Thal asking this is a great way to identify that with some precision and maybe get some ideas on fixing it.
Some thoughts on the observations so far here and elsewhere in default effects left alone
1) mercenary army isn't popular and is weak. We shouldn't be tinkering with it. As Ahriman put it, it seems almost obvious it was only included to preserve the landknecht investment as a unit rather than as a design idea made by Firaxis for some purpose that has a skeleton we could build around. That policy is like eating jelly with no bread. Only the jelly doesn't taste any good either. Or maybe the toast is burnt. I'm not sure where the metaphor goes exactly, but it's bad.
- I'd note that Firaxis actually did a decent job rebuilding Germany when stripping out the landknecht. I just don't think they bothered to just cut the losses and find something productive to do with the policy tree instead.
2) Wealth has too much production or production+gold in it. I'd rather it mostly be about gold and things to do with gold myself. I'd cite things like increasing city connection value or reducing the cost of infrastructure as useful here.
3) Piety's opener doesn't have much to do with the tree (in the same way wealth's opener is powerful enough to just snag it and leave). 5 happiness for tall isn't useful enough that you'd have much use for the tree to go and get it, and for wide, it doesn't make need to use of the rest of the tree. This is not a coherent design structure. I'd rather this tree have more to do with faith and things to spend faith on (but not to the exclusion of beliefs if you don't take the tree). There's a couple picks in here that don't make sense in light of that (theocracy, opener, golden age, and to some extent the "reformation" effects being the constellation of beliefs that are picked for it).
4) Exploration as presently constructed has a very narrow premise. City states in patronage is narrow in the same way that a faith-centered piety tree might be, but city states are often a very useful mechanic now in diplomacy (to prevent or achieve diplomatic victories) and in the same way religion has a lot to do even later on through conquest and diplomacy and any expansion. Peaceful late-game expansion often has little to do with game play (even the mid-game doesn't have much sometimes). I'd be fine with some policies here that help with it as we've been kicking those ideas around as appealing for reasons of micromanagement and psychology preventing settlement for a long time. I might prefer see some of them moved to the tech tree though. The tree should probably have some more naval/coastal advantages that it feels were stripped out to make room for these instead. Contrast that with aesthetics, which is basically the same as default with some extra twists which gives it some general coherence ("this tree is about culture and tourism wins", effectively).
I also don't like the free map and free contact (patronage) policies at all. A tree called "exploration" should be pretty good at encouraging actual exploration and to provide lasting benefits to the units best at it and not just provide for rapid colonisation and the patronage opener makes exploration almost redundant.
5) Rationalism and Wealth both have some duds or dud-feel policies. This is less true of liberty or tradition (note that there are not many comments on tradition and mostly positive comments on liberty). I think this might be because there was a lot more argument ahead of time on which to base ideas for liberty/tradition and even honor for balance and some sense of consensus was emerging on the design. Even as some people might be unhappy with some changes or effects, it was generally quite good. What work may be there is probably manageable numbers wrangling rather than design scrapping and coherence. (I could see moving the 5 happy from piety over to liberty at some point, but that's about it).
Piety doesn't quite get as much a pass, but that's mostly because I don't think any of us have very good ideas that we could do easily in this mod. There's no consensus and some confusion about the design intersection of beliefs and the policies. I think that's kind of expected. We'd do well to find the things we do like and start from there.
Other mid-game trees hadn't gotten as much scrutiny and I'd say that feeds into the feeling that they're not quite as fleshed out in what they do, in that they have some duplicated effects or weak effects that aren't worth investment alongside powerful effects that are. It might have been best to go ahead and run something out there to start the ball rolling somewhere and fix it as it goes along with in-game input (this is a beta after all we're playing with), but it feels rushed a bit or experimental rather than an invested structure that we could flesh out easily.
I'm not entirely sure where some of the ideas were headed without seeing the discourse that went into it to be able to offer as much constructive advice. So I'm sorry if it comes off as destructive.
, as that helps me get more policies. +3 in the Capital, +1 for cities, free 
. Any policy that gives a boost, but isn't out-of-whack with the rest of the choices, is fair game.
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