qmake -r is slow (due to not being parallelized). in some cases, it also produces subtly different effects than a plain qmake/make. the reliability problems of non-recursive qmake known from qt4 do not exist in qt5 any more.

therefore, qmake -r should not be used.

for fresh build trees, a simple qmake/make is sufficient.
for every other case where a qmake run must be enforced, the qmake call must be followed by "make qmake_all", which does the recursion via make.