UV light does not just create repairable dimers in DNA bases, it can and does rip DNA apart. Enough exposure would cause more than enough irreparable damage to kill the cell and 99% of the cell being destroyed is certainly not salvageable.
The Delta flight is cheaper. But check a bag at a cost of $25 for the first checked bag each way on Delta, and your total fare climbs to $256 -- more than the cost of the Southwest flight, which includes free first and second checked bags. Add a second checked bag for $35 each way on the Delta flight, and you'll pay a whopping $326.
The new fee applies only to tickets purchased after December 6 for flights on or after April 10, 2018. Before the change, basic economy passengers were afforded one free checked bag on these flights, the same as Delta's main cabin passengers. Basic economy passengers traveling before April 10 will still get the free checked bag.