Not at all. It depends on CPU you buy -> but yes i bought no CPU for mining -> but i use my mining rig CPU´s for mining 
But a Ryzen CPU is worse to buy for mining -> example my R9 3900 (bought for chia plotting) cost me 400€ and the CPU give between 2 - 5€ a day -> 100 - 200 days to touch the ROI -> what GPU can give us a ROI between 100 - 200 days?
But i am agree, i would never build a RIG only for CPU mining -> but you can push the income of an rig a little bit.
By the way i am mining with profitswitching on zergpool and let me pay in BTC -> over 0,5BTC mined by my CPU´s in the last years.
A little unfair comparison between the CPU and GPU days to ROI But a Ryzen CPU is worse to buy for mining -> example my R9 3900 (bought for chia plotting) cost me 400€ and the CPU give between 2 - 5€ a day -> 100 - 200 days to touch the ROI -> what GPU can give us a ROI between 100 - 200 days?
But i am agree, i would never build a RIG only for CPU mining -> but you can push the income of an rig a little bit.
By the way i am mining with profitswitching on zergpool and let me pay in BTC -> over 0,5BTC mined by my CPU´s in the last years.
Remember where we are right now, the GPU prices are higher than normal due to very high demand unlike the CPUs. But there is information that AMD Ryzen gaming PCs and CPUs are being targeted by cryptocurrency miners lately. So obviously if the demand for the CPUs rises more, the days to ROI are going to be stretched further just like the case with GPUs