What I will say is that:

I don't think it's necessarily valid to assume the rest of the cast made as much as 1/3 of what Stewart made.

Spiner (the second highest billing of the cast) made only 55% of what Stewart made in the Insurrection based on OP's post. Did everyone else made 33%? Maybe... but maybe not.

In any event. What people sometimes fail to appreciate: That number is not what the actor makes. That is their salary. They will have to pay their agents/publicists/accountants/lawyers and that can be anywhere from 15-30% or more. They have to pay any legal fees for their lawyers who review their contracts. I'm not sure what deductions were in place in Hollywood in the early 90s, but now they have to pay several deductions like social security and medicare.

So let's say that your 2.23m conservatively nets down to $1.65m before income taxes even without most deductions.

Now let's note that this is payment for their involvement in TNG from 1987 through 2002. That's $110,000 per year for 15 years of variously 1987 dollars through 2002 dollars (with most of the money coming in later years).

Someone who makes $110,000 pre-tax per year for their entire career (average working life is about 40 years) might be seen as some to be "rich" (in 2024, in the biggest cities, I feel that this is just on the cusp of being within "upper middle class", particularly if they are the only income earner in a family of more than just themselves).

You also have to bear in mind that the cost of living in that area is significantly higher than the cost of living in most of America, meaning their money would have gotten eaten up faster than the average person. Many actors also have to spend more money than the average person on things just to keep up appearances since their looks are often their livelihood like dietitians or private chefs, personal trainers and fitness costs, surgery and procedures, fancier and more clothes and jewellery than the average person might buy, etc.

Now, I am sure the cast other than Stewart has made a lot of money through Trek via conventions - I have no idea how many they do in a year and what they are paid (I do understand there's a range), so perhaps they are able to make a comfortable $100k a year still off of Trek. They also do other acting work, and some of them direct.

The bottom line is that I have little doubt they are comfortable because of Trek. I am not sure that most of them have fortunes because of Trek. Though I suppose it depends on how you define that word.