It's kind of weird to compare PPL certification - which requires ~40 hours of logged flight time and a written test - with a hobby rocket certification. They're not even in the same class of training or risk. It's like comparing an endorsement on your driver's license for motorcycles with getting a class A CDL with all the endorsements.
True, they are completely incomparable. One requires training time and one requires zero. And further, one allows flight over people, one allows flight in deserted field into waivered airspace.
The certification process seems significantly underdeveloped if safety and accountability are the actual goals. You can do a lot of damage with an L1 motor in a rocket that doesn't separate or where the fins fall off in flight, or where your stability calc was wrong. I guess that's what RSO's are for, a final sanity check to save everyone's bacon. Side note, I'd be curious how often rockets get rejected at the table?
Still, there is a very large space between the minimum requirements demonstrated to buy an L1 motor and the upper limit of what you can do on L1 with no training or certification along the way. That leaves people free to experiment and do cool things, which is awesome, but is directly in opposition to safety checks and balances which is the purpose of a certification program. While we are talking about aviation, PPL, single engine, multi engine, tail wheel, type ratings, commercial, instructor, ATP etc are all separate endorsements or ratings that require additional training and demonstrated proficiency. Should you have to prove you are DD capable with your rocket before allowing it unsupervised? I don't know. I think the dollar cost of failure might be enough incentive...
As a new guy to this hobby, I see the certification process mostly as something lobbyists to federal organizations can point to and say, "See, look at our processes, we are safe and accountable. We've got membership, rules, and different levels. Please don't restrict sales, transportation and shipping of our propellant and allow us to easily acquire airspace waivers."
And that's totally fine. Freedom is a great thing if handled responsibly. But I don't think people should be discouraged from going above the bare minimums on their L1 cert. That just makes the goal of L1 cert to "get in the door first" then experiment later when no one is watching. Seems counter to good safety culture.