I have to agree with him, multi pose plastic kits really were the best. Matching bitz and bobs from different sprues with relative ease were great fun. It's a shame that it seems to be going away again at the moment.
I saw one of my mates had got a boxed set recently, when he told me that he couldn't just swap the arms around I was gobsmaked. The monopose miniatures ruin a big part of what I enjoyed about collecting armies.
I had the same feeling when I got me a box of Primaris to check them out. Considering that I usually play Space Wolves where I can just bash kits with the regular Marines and get something fun, this was just sad. Two sprues of 5 dudes and basically the only thing I can easily customize on each of the 5 is what gun they hold and what head goes on which dude. Didn't buy a second box of them.