TabletopTweaks-Reworks VS SpellbookMerge

That's how the original Mythic Sneak Attack works. TTT Reworks changes it to a die increase so d6s become d8s; or Knife Master's d8s become d10s.

TTT Reworks has a number of balance tweaks, including changes to the Perception 2 Trick. Pro is it gets rid of the 3-feat tax by eliminating the three extra crit feats; con is it also gets rid of the +1 crit multiplier bonus.

Release v1.2.5 · Vek17/TabletopTweaks-Reworks · GitHub

FYI the TTT Reworks mod rebalances Trickster so you might find it more fun to be, well, less OP.

[The TTT Reworks addon is optional and has homebrew rules which rebalances Mythics. Some abilities are made more powerful while others are nerfed.]

FYI the SpellbookMerge mod was recently updated for WotR EE; it adds a bunch of new options, including bard+Azata. Why should Angels and Liches be the only ones who get that perk? :) Also the TTT Reworks mod makes a few minor improvements to Azata; e.g., "Incredible Might now grants a mythic bonus instead of a morale bonus" so it will stack with other buffs.

Mythic Reworks - Homebrew changes to Mythic Paths.

If you're on PC, there's a Spellbook Merge mod which adds a ton of new combos, which should also increase spell slots. The mod hasn't been updated since March, though, so caveat emptor; neither the mod author nor I accept responsibility if it bricks your game, opens a hell portal, etc. :)

Doesn't let you merge everything with anything but: https://github.com/vikigenius/SpellbookMerge

Spellbook merging is a big part of what makes an Angel Crusader KC so good. It's not an option for Warpriests unless you use this mod which adds Aeon+Warpriest merging.

If you got mods, may as well grab Mythic Spellbook Merge to merge anything. Be super busted with a whole new mythic path.

First, there is a mod that dramatically increases available spellbook merges if that's your primary concern. Gives all (early) mythic paths the ability to merge with a fair number of classes, highly recommend for absolutely everyone. Full disclosure, I'm not totally sure what you're on about with the archetype for MT and I don't understand how merging mythic into MT (assuming it affects both books) is anywhere remotely near balanced at all, but feel free to use toybox to give yourself whatever CL/DC/etc you'd like to mess with.

Here is the link.

If you're open to running mods, SpellbookMerge lets Angel merge with Paladin (and arcane classes). While it still doesn't reach the raw casting ability of Oracle/Cleric, Paladin is a classic divine beatstick class, and there's even the whole Radiance thing that incentivizes paladins. If longswords aren't exciting, there's also GreatRadiance that can make it into any other weapon type.

FYI there's also a mod which adds extra spellbook merging options. [Usual caveats about using mods at your own risk etc.]

Also, if you're on PC and feel like the spellbook merging options are too restrictive there's always this option, though some of the books would be extremely broken if merged.