examples both ways, but it seems some great QBs started at least as badly.

It's been a long time since a QB started as baddly and went on to success.  Since QBR has been a stat, the best career by a guyu with a sub-30 rookie QBR (min 4 starts) belongs to Blake Bortles.

The most common examples for stud QBs with rough starts are

• Josh Allen (2018) - who actually had a 49.8 QBR as a rookie, compared to Zach's 28.2
• Peyton Manning (1998) - who threw a ton of interceptions, but was also regularly making big plays... Historically, making big plays AND mistakes is a better predictor of success than not doing either.  Manning was also #23/31 in Passer Rating.  Zach Wilson was #31/31

The better examples are 

• Troy Aikman (1989) - was #27 in pass yards/game and #27/27 in passer rating
• Steve Young (1985) - hard to get exact match stats since he was in a different league... but it was pretty abysmal

If you want a more recent example, the best hope is

• Jalen Hurts - his per game stats are tough since he often played a snap or two, but he averaged 230 pass yards/start which would have put him #23, and his passer rating would have had him #32/36 (if he had enough snaps) and his QBR was only 33.8