After a few CWL weeks, here's what stopped the most 3-stars on my TH17 bases:

1. Offset the Town Hall so Root Riders can't path straight through the core.
2. Put Giant Bombs in pairs on the obvious hog/rider lane, not inside compartments.
3. Keep Inferno Towers on single-target for war; multi only if your league is air-heavy.
4. Swap layouts every war — a base with thousands of copies is already "burnt".

What works for you? Asking because I'm sorting layouts by TH for a free iOS app (unofficial, not affiliated with Supercell) — link if useful: https://apps.apple.com/app/apple-store/id6804564319?pt=2720803&ct=shitjustworks_en4&mt=8