"Lower tier " oils you have run...

Lowest tier oil I've used is probably supertech conventional, back when they still made such an oil.

I've also used Quaker State green bottle which at the time wasn't much more expensive and also occupied bottom shelf real estate.

Also used to use a bit of the Mobil Super 5000 product. Wish it was still available at local Walmart.
I used Mobil 5000 with a Motorcraft filter in my old 2000 Expedition with a 5.4 2 valve the whole time I had it. Got rid of it with 170k on the clock in 2010 after having exactly zero power train issues.
It met the standards of the time and I rarely went much over a 5k mile OCI because it spent a fair amount of time in city driving.
The synthetic sold as Orschelins House Brand in synthetic,Amalie, Harvest King Synthetic from Atwood's, Napa and Valvoline Synthetic.

To be fair,they were only used with less than 20 percent oil life just to get my through a couple of weeks when weather was awful and no filter was changed as I did the fill and spill through dipstick.
Actually a safe way to flush without flushing per se.
supertec 10w30 in both tundra and highlander since new. highlander hit 220k recently. supertec synth that is and also in my silverado for the last 50k
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I don't think I've ever run anything not a lower tier oil. Once, I was in Family dollar by my work. They had "American" brand oil (something like that) for $1 a quart. Had Warren Distribution on the back and the API label (SN.) So, same as Supertech, Kirkland, Amazon Basics, etc. They had 3 quarts of 5w-30 and 3 quarts of 10W-30 left. Paid my $6 and did the oil change on the old GMC pickup we had. In it went. About as low tier as it gets :)
When my local KMart closed I bought out their remaining stock of Super S Multi-Flo 5w20 and ran it in the CR-V it worked just fine.
Ironically, my wife and I were in Florida visiting her parents right when all the K-Marts were closing. Ran up there for something (curtain rod I think, I was helping fix stuff around house) and saw that. Called them while standing in store and asked if they needed an oil change. They were due, so I grabbed the last 5 quarts they had of the 5W-20 and grabbed a filter at autozone on way to the house. Their Camry didn't seem to have any issues with it.
My takeaway from reading, here and elsewhere, is that any API or Dexos oil is fine if you change it regularly, but if you're going to stretch your interval, you'd want a more premium oil. Obviously there is not universal agreement on this point, but it seems like a reasonable conclusion.

Since I change at 3000, I buy Kirkland (Warren) and feel fine about it.
This right here.
Used to use DA Speed Sport oil in my British sports cars way back in the '60s. Apparently that company is still in business and making boutique oil products. Too bad I don't still have an intrepid Lucas energized Jag/TR/MG/AH to dump some into.

DA Speed Sport.jpg
My 2016 wrangler's pentastar has been happy with conventional formula shell 5w20. I got a deal on a bunch of cases a few years ago. I like the 1qrt bottles because the jeep takes 6qrts and most oils are sold in 5qrt jugs now.
Interesting topic for sure. I have often asked myself about contrasting maintenance plans. Slightly thicker oil, much cheaper, off label, but still known to be of high quality. More frequent OCIs.

Vs extended OCIs with premium, expensive motor oils.

I am inclined to use very thin motor oil. As absolutely thin as possible, but surely as thick as necessary.

I have mostly used 0W16 lately (even thinner) everything from cheapo Citgo 0W16 to ultra premium High Performance Lubricants 0W16. My sensabilities take me to the expensive stuff. But what if ?
Supertech is a fine oil.

I can remember Kragen selling a generic, plain black and white label oil.10W30 Synthetic. $3/qt. And I can remember being an early user of Red Line. How about Exxon Superflo in the red bottle.