I wonder if CBP questions Greeks about their intentions a bit more than visitors from other VWP European countries due to the economic problems in Greece.

I thought about it as well, but I've been visiting for 4 years now and it's only gotten very bad financially the last couple years in Greece. The laws that apply are the same ones for all countries of the European Union except for Germany that can also have Global Entry.

To be honest, since I was born and raised in Germany, I have the right to get dual citizenship and also have German rights, but I've never thought I would need to, lol. But that's a whole different story and not worth the hassle just to be able to visit for a few weeks.

Hopefully after presenting the B1/B2 it will be a little better. Worst case, I will just do it from preclearance airports so that I can get it over with and not be questioned after an exhausting 20 hour flight

Excuse me, but how is ATH to MSP an exhausting twenty hour flight? AMS/CDG/LHR to MSP is about eight hours and ATH to these airports should only be about four hours. You don't need an eight hour connection at AMS/CDG/LHR and, in fact, it would be pretty ahrd to schedule flights with eight hours in these airports. The three airports I listed here are the only choices for nonstop flights from Europe on legacy carriers; if you connect in the USA, you wouldn't go through CBP at MSP.

Not everyone flying from Greece is either from Athens or originating trips from ATH on one-stop routings. From a bit outside Chicago to parts of Greece where some of my acquaintances go, some trips from door to door take close to twenty hours.

That. My trip was

SKG - ATH 11:55pm - 12:45am (+1 day)
ATH - CDG 06:30am - 09:00am
CDG - MSP 10:35am - 12:59pm (Greek time 8:59pm)

so it's pretty much 21 hours just for these particular flights.

Anyway, sometimes I do STR - ATL, ATL - MSP because my parents live in Germany, but that's still a good 15 hours sometimes.

Yes, but 20 < 24. OP mentioned doing CBP at MSP, so he's not making connections in the USA.

I've seen 27 hours frequently enough in one direction at least for some U.S.-Greek trips, so 20-24 or more hours is well possible from Greece, a country where a part of the population lives on islands.

Making connections on the way from Greece to the USA and clearing CBP at MSP, the trip can still be long and in the time range mentioned by the OP.

Keep in mind that when the OP is using the word "flight", the reference is to a trip with multiple flights rather than just one flight. You know well enough that there is no non-stop scheduled commercial passenger flight service from even ATH to MSP -- never seen it in my decades of flying in and out of MSP. And even just for ATH to MSP via existing connections with CBP clearance done in MSP, 14-17 hours is rather common; but once someone adds a Greek airport other than ATH to the picture, it frequently enough hits the 17-23 hour range for flights inclusive of transit time.

Please check the third post above this one. It can be 21 hours and going through CBP in MSP. I don't fly always like that, but sometimes I have no better option