Plenty of lighting experience here, as we typically have issues lighting aircraft hangars.
1) T-12 Fluorescent fixtures don't necessarily use conventional ballasts, they can and often do use electronic ballasts, and when elec ballasts are used, along with quality T-12 bulbs, the "luminous efficacy" is essentially similar to T-5 or T-8 or LED, at 80 to 100 lumens per watt, depending on color temperature.
2) T-12 Fluorescent bulbs "can" be every bit, or even more efficient in real world use than T-8's. The modern bulbs have to meet certain standards.
3) In general, Fluorescent fixtures with acceptable color temperatures are still slightly more efficient than similar LED's. The best practical LED's hover around 80 lumens per watt. I know of no LED's that can achieve a 3200K color temp and 100 L/W in real world use.
4) Properly chosen T-12 fixtures have higher brightness than T-8's, but they also consume more power T-12=40W, T-8=32W.
5) LED's will cost many times more than quality Fluorescent fixtures. But, as mentioned above, they work very well in cold climates.