If the 737 had low altitude handling problems, don't you think someone would have noticed by now?
Wikipedia:
The 737 is operated by more than 500 airlines, flying to 1,200 destinations in 190 countries. With over 8,000 aircraft ordered, over 6,000 delivered, and over 4,500 still in service, at any given time there are on average 1,250 airborne worldwide. On average, somewhere in the world, a 737 takes off or lands every five seconds.[7] Since entering service in 1968, the 737 has carried over 12 billion passengers over 120 billion km (65 billion nm), and has accumulated more than 296 million hours in the air. The 737 represents more than 25% of the worldwide fleet of large commercial jet airliners.[7][107]