How rare is it that I have "foundblocks 1" on my antminer d3??
I've been running it since the start of December on my 19.3 gh/s d3? It makes me wonder if I should have just solo mined because I would have just earned 1.9 Dash coins instead of what I have now (less than .41 dash)

It's not rare at all. I get several. Unfortunately if you were not on the pool you would not have those "found blocks".