Codex vs Index Armies

Well the Chapter Approved book being released next month covers that - from what I understand it gives some abilities and relics and fluffy warlord traits to the non-codex armies to help hold them over, in addition to covering sweeping updates to the points costs of models and equipment across the entire game. Its basically the 40k version of the Generals Handbook for AoS, which will be a yearly release to sort of "soft reset" the game as it starts to swing out of balance over time.

But short answer - no, they are certainly not balanced. There are a few ways to help mitigate that though in casual games. I don't bring relics and limit my use of strategems to a couple that I mention before the game. If I know I'm playing an index army beforehand, i sometimes bring weirder/less optimal units too.

You could also just really encourage people to self-regulate. The index buffs are good, but don't seem generally game breaking unless someone is trying to create the most utterly powerful build possible.

I’ve been operating my Death Guard with a “no primarch” rule until everything settles and other armies have realistic options to deal with those big bastards . Tyler has suggested a “no lord of war” rule as well that I think goes a long way to making the games more balanced.

You could also ban battle forged armies. I think playing a single faction army force cuts out a lot of the abuses open to Chaos, the imperium, and to a degree Tyranids. Death Guard get a lot scarier with warp time, which is why GW took that particular toy away from us.

These are just suggestions if a problem even arises. One of the things I like about this group is that 90% of the people playing here seem to be looking to have a good game, not find overpowered loopholes.