It seems like one possible way to offset Marig weaknesses as you have pointed out is to do the following:
1. Take good scales (order for money, growth for old mages and money and magic +1 for research)
2. Take "crap" bless on rainbow pretender. Marig. I guess can be played in two extremes, either great bless that gives you crap scales and no diversity in magic and then you have to rush rush rush for in the end game you'll be toast or with "crap" bless as I suggest. Take 4E, 4A, 4D, 4N on a dormant rainbow mage.
3. Fire can be used for economy and summons, not only evoc. plus FftS is one of the best artillery spells.
Ahmm, I kinda like to stick to a few nations that I like, no matter their perceived strengths. Now Pythium is by all accounts a strong nation but it took me a long while to get used to it and play it effectively.
What I'm saying is, if you like this nation, I'm sure you'll find the way to make it rock, so don't give up
