Underblock is a ridiculous basis for compensation. It does not motivate crews to be efficient, nor to be on time. It just makes them fly faster making for waste. Sometimes being underblock means being on time, but just as often it means arriving early, which is not of any particular benefit to the company, but for which crews are equally rewarded. At the same time it doesn't necessarily generate on time performance. You can be 30 minutes late at destination because you took an hour to get lunch on a 45 minute turn, but still get premium if you are underblock. That's crazy.
Beyond wasting gas by flying full out, crews have no control over the factors that contribute to earning premium. Whether you get premium has more to do with wx, ATC, rampers, ramp control, etc. than anything within a pilot's control. It doesn't reward the guys and gals who show real hustle out there, it just rewards those with good luck, good timing and a willingness to burn extra gas to go Mach .83.
Smartest thing to do is get rid of premium pay. No I didn't say take money from the pilots, just get rid of premium pay. It's not hard to figure out the annual average of premium pay and to roll it into the pilots' pay rates. No net cost to the company and no loss to the pilots. And no, that is not as substitue for any pay rate increases the pilots can negotiate. It is just a way to stop the wasteful practices that premium pay encourages.