Reason suggests that evolution designed us to cope with one or two concussions in life.  The brain has good regenerative capacity for a couple of significant concussions.  There is evidence that repetitive concussions do cause cumulative brain damage but this may not be apparent until middle or old age.  Mohammed Ali is a classic example from boxing.

The worry with heading in soccer is that even though the impacts are sub-concussive there are so many of them over so many years (depending on career length), moreso if players start heading whilst still children.  Even though the balls are more light weight (FIFA deliberately did this because of concern over cases like Jeff Astle), they are kicked with much more speed and power and players whip their heads to connect with the ball much more, and there is just a lot more heading than in past eras

There are Dutch studies of both amateurs and professional soccer players that showed a correlation between poorer performance on cognitive testing and players who headed the ball a lot versus midfielders who had a career where they headed the ball much less.

So if I played soccer or had children playing it - I would want to be a midfielder who only occasionally had to header the ball.