I'm chalking up last year (without Grubb) to the type of QB we had. Though I really never like dumping the blame soley on one player when so many other coaches and players are involved. But I don't see Grubb, especially if he has success, being with DeBoer forever. I'd love to see DeBoer call a game himself just to see what he'd do. There have been a lot of coaches who've done that.
I hope you're right and it is like McCartney and Lennon and not Brooks N Dunn. Who together, was hall of fame worthy, but separate, just so so.
At Fresno as OC, CKD took an O that was ranked 12 in 2016 to 9th, then 4th, in 2017-18 before he left for Indiana as OC for one year, 2019, and led them to 3rd in the B10 in total O after being ranked 7th the year before, then 10th in 2020, 14th in 2021 after DeBoer. Don’t know if the difference was because of personnel or the OC or ???. (Sheridan replaced DeBoer as OC

.) So, CKD has succeeded without RG as OC.
Grubb was never the OC at Sioux Falls under DeBoer, but was on the staff as OL & RGC for 3 of DeBoer's 5 years as HC. As Fresno OC, he led them to a total offense ranking of 8, 1, 1 in 2019-2021. The last 2 years as CKD’s OC, who returned as HC in 2020. So, the more pertinent question might be how good is RG without CKD? He was mediocre under Tedford (4th to 8th as OC) and fired by Seattle in his only 2 years without DeBoer, but he’s been spectacular with him: 1 & 1 at FS, 1 & 3 at Wash in 2022-2023, then 16-0 and SEC's number 1 O in 2025 at Alabama.