Take a closer look. I don’t think Princeton is good but compared to ND they are. You entirely going by brand names. The very quad system you are preaching sorts most of Princeton’s opponents fairly similarly to NDs. Both teams are 6-0 vs Q4. Again - Princeton is 4-3 vs Q3 while ND is 1-3. Princeton is 2-1 vs Q2 while ND is 1-3. Your right - ND went 0-4 vs Q1 while Princeton didn’t play any Q1s. So basically what your saying is getting blown out once, and losing by 11, 9 and 4 to top teams is not only better than going 3-0 vs Q3 instead, but it’s so much better that it even makes up for having a 2-6 record vs Q2-Q3 compared to Princeton’s 6-4 record.
Sorts them fairly similarly?
Notre Dame's opponents in the NET Top 100
2 - @Duke (8 pt loss)
3 - (n)Houston (11 pt loss)
27 - @Georgia (21 pt loss)
38 - UNC (1 pt loss)
40 - (n)Creighton (4 pt loss)
79 - @Georgetown (21 pt win)
83 - (n)Rutgers (1 pt loss)
Princeton's opponents in the NET Top 100
83 - (n)Rutgers (1 pt win)
86 - @St. Joseph's (8 pt win)
Meanwhile, at the bottom of their respective lists...
Notre Dame's opponents ranked 250+
272 - Stonehill (29 pt win)
289 - North Dakota (17 pt win)
333 - Buffalo (9 pt win)
338 - Le Moyne (27 pt win)
Princeton's opponents ranked 250+
269 - Harvard (4 pt win)
278 - Dartmouth (1 pt win)
284 - Monmouth (4 pt win)
291 - Iona (1 pt win)
319 - Portland (27 pt win)
Princeton has been in 4 life-and-death battles with teams rated 250-300.
Notre Dame has a worse record but is a stronger team. Heads up on a neutral floor, it'd likely be Notre Dame (-5.5), Princeton (+5.5).
And looking ahead.... Notre Dame has 7 more NET Top 100 teams to play, and Princeton has 2. The ACC may be down, but it's still a lot stronger conference than the Ivy.