Unless changed in beta...
It seems to me the road classes appear in Road theme too late, at too high zoom levels, especially secondaries..
Primaries at Z9
Secondaries at Z12
Tertiaries at Z13
IF you choose at Z11 the area NE to the City of Brno ( Czech Republic ), with Adamov or Boskovice near SW map corner, there is literally near nothing on the map. No roads but few rivers and eventually hill shading.
Imagine much less populated countries than those in Europe, with sparse road networls. In such a case, finding roads can become funny smartphone game.... :-)
I would switch start of appearance from 9-12-13 to 8-10-12