I am fine with whatever you are fine with. Just want to clarify what your choices actually are...
Yes - there are numerous € 44.97 saver fares for your date: With scheduled flight arrival at 7:20, the 8:30 departure at this fare is extremely iffy even if the flight is on time, no one needs to hit the restroom, etc.
The next such cheap fare at 9:54 is a safer bet as long as your flight gets in less than an hour late. Is that the one you planned to book? That said, the train does NOT arrive at the main Cologne train station; you will need to transfer at the Messe-Deutz station across the river, where your train dropped you, to get back to the main part of town.
The next such cheap fare at 9:57 gets you directly to the main station - at 12:06, a ride of 2+ hours.
Whichever you choose: forfeiture of the ticket €44.97 fare because of a delay leaves you at the airport and means either paying €100+ each to Cologne, OR getting the Quer durchs Land ticket at €69, as you point out, resulting in a €114 travel day. And also as you point out, it is not for the fast trains. So...
You missed that first 8:30 train? Next option for the slower regional trains on the QdL ticket - which leave from a different airport rail station - is at 9:24. This is not a direct trip - it's a 2-train sequence. So after stopping in Bacharach, Oberwesel and Boppard, your train terminates in Koblenz. There you change to the 2nd train after a 22-minute layover. Total travel time is 3+ hours, with arrival at 12:28, some 5+ hours after your scheduled landing time.
The alternative - heading straight to one of the MRV towns for a stay there:
The same 9:24 train is DIRECT to the MRV town you choose. Let's say it's Bacharach...which takes 56 minutes. Arrive there at 10:20.
There is no advance-sale ticket to pre-purchase or forfeit. There is no transfer to make on your way. There is no schedule to keep - no matter what time you get to the Regionalbahnhof at FRA, you can get a ticket and leave on the next train. You can use the QdL ticket at €69, but the wiser choice for this trip is the RMV Gruppentageskarte. Buy it on the spot at the station.