Effect of light intensity on the frequency of stomata
You are misunderstanding photoelecric effect.

Intensity of light does not have effect on maximal kinetic energy of individual ejected electrons. Maximal kinetic energy of ejected electron is determined by energy it can get from single photon which is in turn determined by frequency of light.

However, intensity of light definitely does have effect on number of ejected electrons. More incident photons (higher intensity of light) result in more ejected electrons (and higher measured electric current).

In photosynthesis number of utilized photons is more important than their energy. Photon either does have enough energy for separating the electron (e.g. red or blue light) or it does not (e.g. infrared light). If a photon with energy higher than needed (e.g. blue light) is captured then the excess energy dissipates to heat.