For x264 that is true, HEVC which is also mentioned is much slower. For a 4k source transcoding can take more than a second per frame. For a normal movie this can quickly result in encoding times of more than a day.

Another problem is that you have to encode the movie for each codec profile times the number of different bitrates per profile. The article mentions four profiles (VC1, H.264/AVC Baseline, H.264/AVC Main and HEVC) and bitrates ranging from 100 kbps to 16 Mbps. Assuming now there are 20 different bitrates per code you already get 4*20 => 80 encoded copies per source. But of course this can be solved by parallelism.