No, I most definitely would not agree that mid-20th century cooling was the result of solar variation. TSI was actually increasing up to the Modern Maximum around 1960. TSI began to slightly decrease around 1980. The flat-to-cooling temps from around 1945 to about 1975 were likely the result of the combined effects of increased atmospheric albedo (air pollution), and simultaneous negative phases of the PDO and AMO.

Again, solar variation (on relevant time scales) has surprising little impact on GMST.

In regard to the increase in GMST during the instrumental record (which is now over 1ºC) and largely the result of GHG emissions, keep in mind that global temperature only varies about 5º between glacial and interglacial, and did not change much more than 1º over the history of human civilization. We have had a dramatic effect on global temperature in an incredibly short time relative to natural influences.