People keep talking about "waterfall", but I have not seen real, actual "waterfall" in the last 15 years, anywhere. Last time I've seen it was at Microsoft in early 00s, and even there it wasn't super-strict, people just spent their "planning" time prototyping stuff so as not to have to work as hard when the "design" phase ends.

Moreover, for certain types of work (such as, for instance, building platforms) a forced "design" and specification phase would probably be a net benefit. As they say, "half a year of coding can save you two weeks of planning". Except when you also release your shit to users you can't fix your old design mistakes because everyone depends on them now.