You are 100% correct that the quick service bays and lube techs are both a major source of revenue and also headaches for the service manager. The employees in the quick lube bays are usually lower paid hourly employees that are light on experience and/or ability or worse yet, know just enough to be dangerous and are salty they aren't full techs yet and try to do something beyond their abilities and get in over their heads and make a real mess of things. Mistakes get made and you have to have a good supervisor giving everything a once over.
As far as in the main shop, it's hard to find any techs right now (good or otherwise) and a lot of dealers are bumping lube techs to full techs to fill the void even though they aren't ready for the job yet, or offloading some of the easier jobs (paid and warranty both) into the quick lube area to keep the understaffed regular shop with the full technicians from being overloaded... a surefire recipe for mistakes and comebacks.
It's also difficult to find techs that can do proper diagnosis; many of the new hires in the last 5+ years are simply parts changers and have a hard time just following the clearly defined step by step diagnosis procedures in the manufacturer's service instructions. Good luck if you have a real tricky problem that requires advanced diagnosis beyond the scope of the service instructions or requires working with the manufacturer's techline or engineering people to resolve.
It seems to be a lack of techs, and not a simple lack of money to attract good techs-- at least around here. A good tech at a moderately busy dealer service department here can make $110-140k+ a year; $31 minimum hourly rate here in CA for a tech who provides their own tools (minimum pay of double the current minimum wage) even if they have zero ASE certifications, paid for all hours present even for flat rate techs even if it's a slow day and they aren't turning wrenches, and a good tech working at a moderately busy flat rate shop will usually be at 150%+ productivity. I know a few flat rate techs at busy dealers who have averaged 200 hours per 2 week pay period over the last several years, sometimes clocking 28-32 hours per day when the stars line up and they get several back to back "gravy" jobs that are easy and quick to do but are generous on the book time. Several of the really good senior techs make more than their service department managers. Even with pay prospects like that the service department managers can't find qualified people to interview or hire.
The tech shortage and average skill level is bad enough there's at least 2 people in my local area that have advanced diag equipment and software for various vehicle makes and are contracted by multiple dealers to do advanced diag on cars their techs can't figure out, and then give the service manager a list of what needs to be done to fix the vehicles. They do very, very well.
The dealers aren't totally blameless for this tech shortage either, a lot of them fostered toxic work environments for years by playing games with book hours, warranty hours, and benefits which hosed the techs-- and a lot of experienced techs that would be great to have in the shop today don't want to play that game anymore and have moved on to other things.
As far as the relation to this thread... based on the quality of the average tech I've seen hired over the past few years, I expect to see more mistakes being made by service departments in the coming years, rather than less; so expect to find more missing oil caps (and worse) as time goes on.
