I've seen this quite a few times over the years.
Until the last 6 years or so, my friends in the business had no dyno.
So the 15-20 years before it, they put parts on, drove it to the track, tested it and repeated the process.
Sometimes going to Englishtown a few times a week. Back then though only muscle car guys went to the track, now you have civics, luxury cars, suv's and throw some pick up trucks in there. Now the wait is 100 times worse, so it's not so simple.
Helps too to own a shop and not care if you have to take a car apart 50 times to get it the way that's perfect. The average guy doesn't have the time, desire or money to experiment in that manner.
On my last pushrod setup, i dictated what i wanted, i probably should have had him dial the cam back a little so it was a little easier to drive in traffic. Live and learn.
The biggest baddest parts rarely had the best results.
Go figure, one of the cars was a 302 gt40 intake, 65mm tb, valve jobbed gt40x's with an Ecam and ran
[email protected] (i think). With a very experienced driver.