Lava, my lawn is a cornucopia of weeds and bugs, and the back half is in full sun and still doesn't look that bad. I don't know what the issue or solution is, but I doubt pounding pesticides is the answer.
Not sure if Milky Spore works on Cinch bugs but maybe give that a shot. Takes a few years to establish and you're soil is probably too cool this year, but it might be worth a shot next year.
Either that or till it all and plant perennials or wildflowers. Probably cheaper than the money you'll undoubtedly continue to pour into it.