I'd have to run the numbers again, but when I was last commuting daily by rail, Beeston to Derby, it was cheaper for me to just get monthly season tickets September to June, then use my 16-25 Railcard to buy day returns in July and August when the £12 minimum fare didn't apply.
Somebody with a 16-25 or 26-30 Railcard where the discounted fare would be £12 (or actually just below £12) would be better off using their Railcard than getting a season ticket in many cases.
Somebody living in the Southeast leaving after 10am may find a Network Railcard used on daily tickets may be cheaper than a season ticket.
Season tickets usually provide good value, but these 'quirks' irritate me, and is my main gripe with GB rail ticketing. Railcards with minimum fares for 10 months of the year before 9:30am, Railcards with minimum fares for 12 months of the year before 9:30am, Railcards not valid at all before 10am except some local route easements where they're valid from some specific time between 08:23 and 09:59, rovers, GroupSave, TOC-specific group discounts, rangers, regional Railcards, SuperFares, ScotRail Kids For A Quid, Club Avanti, LNER cashback, the fact that mature students can get a 16-25 railcard, Scotland NEC, Unizones, GTR money back guarantee, XC feeless Advance ticket changes, PlusBus, Nothern Duo, gold cards, RailMaster, Rail & Sail, flexipasses, GA pregnant passenger first class upgrades, SeatFrog, carnets, season tickets annual/monthly/weekly, etc etc.
Finding the cheapest ticket for a journey shouldn't require this PhD level of knowledge about the ticketing system. When season tickets are more expensive than buying a return ticket with a Railcard every day, I think the system is broken.
I actually broke the ticket machine when I tried this as well. I bought online ~20 sets of day returns with a Railcard. It printed a dozen or so sets then the printer said 'Out of Order'. Because it was all on one booking reference, I then had to wander over to the ticket office, hand over the printed tickets, and they tore them up and started printing the whole set of ~20 return tickets again. The queue of people which had formed behind me at the ticket machine were not impressed.