One thing nobody ever brings up is the soil temp itself, not just the air. Those pots on a balcony get cooked from the bottom and sides too, so even with shade cloth overhead your roots are basically sitting in a hot tub. Mulching the top and setting the pots inside a bigger pot with dirt or even just a cardboard box around them helps way more than people expect. That said, once butterhead bolts it turns bitter and there's no going back, so calling it on that crop is fair. What worked for me was starting new lettuce seed in July but growing it in the coolest spot I had and harvesting as baby greens at like 3 weeks, before it ever gets the chance to bolt. Chard and Okinawan spinach are solid backups but they're a totally different meal, so it depends if you actually want salad or just want something green.

Had a judge tell me something close at a KCBS event a few years back, said my flat was a little lean and asked what I trimmed to. Same deal as you, I was running a quarter inch because that's what the internet told me, and my flats were coming out like jerky on the back half. Started leaving closer to a half inch on top and maybe a quarter on the bottom, and I also stopped trimming the point so tight. The fat renders down and bastes the flat the whole cook, plus it gives you a little buffer when your fire spikes. Some judges want that cleaner bite but I'd rather lose a point on appearance than serve dry slices.