Keep them going or whack them?

I never recommend it in soil, better dry out and load with good pH water, repeat it 2-3 times, with very light Cal mag feed in the middle. Never water wet pots with soil !!! If it's Coco or hydro setup - go for ! https://www.cocoforcannabis.com/when-and-how-to-flush/ Good luck

I see Phosphorus deficiency and can be heat stress but need to know the humidity and air Temps around the plants. Look up VPD for cannabis so you can get your canopy top Temps and humidity levels close to the sweet spot.

Would a heavy flush do any good at this point?

Link a diary to this grow. Lots of issues but hard to tell what ones are what without knowing anything about your setup.