So CBR RWY30 RNP uses a 3.7 degree approach path. The PAPI uses 3.9 Degrees. 3.7 degrees angle is 6.5% gradient. 3.9 degrees is 6.8% gradient. You are right, you are not flying 5%, but you are certainly not flying less than it.
A 5% gradient is about 2.9 degrees. Probably why ILS glide paths are set to 3 degrees. The approach gradients to ILS runways are surveyed at 2% which is about 1.1 degrees, so flying the glidepath will keep you well above any obstacles.