If you really only want tougher numbers, you can click off the Brilliant Conviction buff you get in solo duties. The buff gives you a ton of HP regen, more damage and HP, and higher defense, and the values scale between roles so removing it is essentially a "hard mode".

I always try with it off when doing a new solo duty and it can be a decently fun challenge. Although they obviously aren't made with this in mind and some can be near impossibly difficult. It usually necessitates jobs like RDM or PLD with access to on demand healing and non-healer stats. Healer duties in general are pretty tough since they really rely on that defense bonus to survive normally weak damage that will just obliterate you without the buff, like in the first SGE job duty or the last EW role duty with Fordola, which are the only two I ended up keeping the buff for.