so started a new fort in 3408, got through the first year and my first non hardcoded migrant wave arrives. The only metals I found so far are galena and sphalerite, so I don't really have a metal industry, I got one artifact, but it is a slate crown worth only 4800, total fortress value just below 70.000, exported wealth 6000. Seems to me that by any reasonable standards this should count as a poor to average number for one year. As usual no real military action yet, so nobody died so far.
The migrant wave I got was 27, so close to the max of 30 and more than my entire fortress population before.
The number of migrants you get is supposed to depend on how well your fortress is doing, which is a great idea, but it seems this is badly off balance. If you don't do anything stupid and provide enough food and basic infrastructure you are already at the max values. You only get smaller migrant waves if half your dwarfs die in the first year, which usually only happens if you want it to. The wealth dependence on migrant waves is completely irrelevant because practically any fort will be scored as maximum wealth no matter whether you make candy armor or just dig a few holes in the ground.
For me this has been an issue since I started playing, about 3404 I think.
I know migrants can have accidents on the way to the fort but I feel this is a very nice feature of the game that has been broken for several updates and only takes changing a few numbers to fix.