Ok, this comparison needs to get qualified, because at face value it's complete bullshit.
The current CP of the BBJ division at Boeing was a squadronmate of mine at the old unit. Interesting stories about delivery flights to China and Saudi, and the gucci lifestyle. That civilian gig is nice indeed. What it is also, is extremely rare of a position and the result of multi-decade networking and hovering around the manufacturer. But of course, that tidbit gets swept under the rug when making these comparisons. To be fair, by VOLUME, manufacturer pilot jobs are to top-4 121 carrier pilot jobs what ONE Miss America pageant is to JCPenney retail positions nationally. It would be rather foolish to put all your eggs in that teeny tiny basket.
Also, a distinction needs to be made between delivery/training pilots and test pilots. I looked into the latter and frankly was rather underwhelmed with their aggregate compensation, for the level of box-checking competitiveness they require on paper. A knuckledragging airline pilot beats the lifetime earnings of a test pilot by quite a bit, with less employer turnover, which is crazy considering we're talking about unstable airline jobs in the first place. Test pilots suffer from the same career nomadism and job loss as company pedestrian engineers, and require willingness to relocate to stay gainfully involved in the industry. This, to avert the alternative of switching to printer toners across the street 'cause mama is sick of moving every 5-7 years because you insist on having 'aerospace' attached to your pedestrian job label. So it's completely inaccurate to suggest test gigs are homestead central. From my conversations with some of them, it seems one becomes a test pilot because one like to geek out about 32nd decimal place validations of the 20th iteration of a 737/Bombadiér, for 90K median. Outside of new materials and avionics, there's nothing flight dynamics relevant about airplanes anymore, but I digress.
At any rate, these jobs are separate and apart from the delivery/training pilot jobs you're probably referring to, which are gucci indeed. Also let's disclose that mother Boeing is indeed undercutting the luxury of that job, as they continue to utilize contract positions (read: walmart benefits) to fly their iron. Cool if you have Uncle Sugar medical/retirement benefits, not so cool if you don't. So things are not all that rosy on that side either, and we're talking about less than 1000 jobs worth of access here between manufacturers, not 5,000+ like in the airlines.
https://www.ainonline.com/aviation-news/2012-09-12/boeing-pilots-protest-use-contractors-train-787-crews
In the end, there's plus and minuses to every job, but to me, a job I can only speak of getting is not a good job at all. Median expectations are what matters in the end; I just don't think it's fair to juxtapose a dozen six-figure equipment manufacturer jobs at any given time to thousands of six figure 121 carrier positions. I think most people here are more likely to get a job with Delta than they are to get a job delivering BBJs for the manufacturer, with otherwise IDENTICAL resumes. We are carbon copies of each other, here in blue Shawshank. But hey, if you got [regular/sugar]daddy/mommy on the board and one of these gigs is waiting for ya after you're done with the 20 year Air Force combat desk deployment kabuki, I'm certainly not gonna hate on that. Talking to my old squadron bud, that's one hell of a job you'd be getting into. Good luck to all.