I’ve always treated max liftoff weight as a guideline more than a rule - a small diameter, low drag rocket over the limit by a bit (on a calm day) will probably be fine, while a lighter but draggy rocket may not work well at all. I’ve used the initial version C/D QJets in heavier, low drag rockets and they’ve worked well, while my Estes 1/200 RTF Saturn V definitely doesn’t like the D motors. What I haven’t tried, other the the SV, is heavy draggy rockets over a C/D QJet.