Would you rather have a 70% win rate with 1:0.5 RR, or a 35% win rate with 1:3 RR?"

I'd take the 35% with 1:3. Run the math: 70% at 0.5R is (0.7 × 0.5) − (0.3 × 1) = +0.05R per trade, barely positive, and costs can wipe it out. 35% at 3R is (0.35 × 3) − (0.65 × 1) = +0.4R per trade.