Should my non-showdown winnings be much better than they are?
The only thing that matters is the green line.
Among the long term winners here, you will find all kinds of red NSD lines. Mine goes straight up at 2BB/100 on average, but many others go straight down at -2 or 3 BB/100 and those players are just as profitable as I am.
It's a question of style, but there is no style that clearly outperforms the others. So as long as your green line goes up, no need to worry about the others.
Does this mean I am playing too many hands?
What more info do I need to provide to correctly form an answer?
That would require more detailed stats like vpip/pfr/steal%/...
Also, you want to check your positional stats, i.e. the same graphs and stats by filtering for EP, MP, CO, BTN and the blinds.