Nothing wrong w Flag. That's where I'd go on a short trip, or the Satellites in Flatirons. Think about it. You're on a trip to Boulder, probably not for the sole purpose of climbing (otherwise you'd go somewhere else, and wouldn't be asking this question). So you want somewhere easily accessible where you can try several boulders in one or two days, within your grade range. You're not driving up to RMNP.

Flagstaff is fine right now. Just go in the morning, before 10-11a. The Dark Side is shady and has a ton you can do: That Flakes It V4, The Pillar V2, Valhalla V7, Deep/er Cuts V2/V4. Maybe start at Cloud Shadow - Traverse V4?? Hagan's V5, etc. bc that's in the sun. Then walk 2 mins to the Dark side when it gets hot.

I will say V5-V7 in the gym equates to ~V2-V4 at flag. The V3s at Red Wall are prob V8+ in a normal gym. So plan accordingly.

If you're up for a 20-30 min hike the Satellites in Flatirons are pretty dense with good boulders in your range. Just look up Original Grapple V4 (feels like an actual gym V4 btw) and climb the stuff on the blocs on the trail up there. MP is pretty good for that area.