A couple of points:
Firstly, modern airborne radar have Turbulence mode as well as weather (WX+T). This is real time information that is not available on a controller’s overlay. The rainfall intensity doesn’t necessarily have to be red for there to be sufficient vertical velocity to indicate turbulence (magenta) on the flight crew’s display.
Further, with convective weather, the suituation can change very quickly. The preceding aircraft may very well have not had any adverse indications at the time. It’s very inappropriate for the controller to suggest that since the others went through it, you should too! You only need to look at the Delta 191 accident at DFW. The light jet that flew through the same cell just moments prior to DAL191 reported a smooth ride..
My 2 cents.