Congratulations, you've rediscovered an old Italian technique for improving dicey coffees. You get lots of extra points for tasting the early part of the shot too.
But while your instincts are great, your data is erroneous -- it's normal for shots to start black for a the first few seconds.
If you use a medium or lighter roast than Peets, you'll still get a very powerful taste when you taste the first few drops, but it will taste more balanced, and you'll get more blah shots if you let it go into the drip tray. However, caramelized sugars, which create the sweetness in espresso, are less soluble than some of these acidic and bitter fractions, so the first few drops will never be fully balanced.
Peets is not really state of the art for home espresso. Our favorite roasters are listed
here.