The 1400 has a top clockspeed of 3.4GHZ and the 2400G a top clockspeed of 3.9GHZ,ie,around 15% it seems,but we don't know for sure if the 2400G will consistently hit 3.9GHZ though. The increase in CB ST scores is 11% though.
The 1400 base clockspeed is 3.2GHZ and the 2400G has a base clockspeed of 3.6GHZ,ie,12.5% but the score goes up by 12.5% so it seems at least for CB its not really affected by the reduction in L3 cache.
I also suspect for gaming having one CCX instead of two will actually help mitigate any potential loss in performance,and should make performance with a dGPU less dependent on higher speed RAM IMHO OFC.
Edit!!
Something else which is interesting too.
The Ryzen 3 2200G is a 3.5GHZ~3.7GHZ part and the Ryzen 3 1200 is a 3.1GHZ to 3.4GHZ part and the Ryzen 5 1400 is a 3.2GHZ to 3.4GHZ part.
Look at the CB ST score - the 2200G is 5% faster for 9% increase in clockspeeds(assuming it can hit is max Turbo clockspeed). The Ryzen 3 1200 and Ryzen 5 1400 are hitting their max boost clockspeeds though.
Now look at the increase in base clockspeeds of the 2200G over the 1200,ie,around 13% extra clockspeed. The increase in performance is between 7% to 15% in MT scores.
At least comparing the Ryzen 3 1200 and 2200G,it looks like the reduction to 4MB of L3 cache from 8MB has not done much.