Out of curiosity,
which lower level wizard spells do you think scale particularly well, the damage ones? Also druid, but I only did tests on a lvl 20 multiclass wizard. The lvl 2 unique raw missile seems to be doing particulary well, and so does the lvl 1 missile simply because it cannot miss, but I'm not too happy about either the lvl 3 or lvl 4 missiles (target weird armor, and are higher level so don't get that many extra missiles) - not sure if they are actually scale up to be better than fireball/shadowflame. I guess the lvl 2 necrotic lance is also in a good spot due to double scaling, but also compete with the draining missile or the infamously good combusting wounds + miasma.
Forgot to test - do wall of flame's individual hits do accuracy rolls/benefit from ring of flame? I slept on this spell, and it seems to be better than wall of force unless something is immune.
Also, penetration scaling is...what it is. I still think that a blood mage multiclass with something that gives tenacious works competitively with a single class considering difficulty mods, extra sustain and penetration seems to be a huge benefit, especially if a single empowered high level ability does not solve problems (which is the case on podt upscaled++, like hardcore deadfire).
At the end of the day, one big axe does the job better unless you use multihitting spells & combusting wounds, or there's enough enemies to use a shadowflame or something like that (I'm really unsure what the devs were thinking about spell penetration & its scaling, getting value out of spells requires a lot more minmaxing than weapons, especially on higher difficulties)