I've had a similar situation, and have had the 24-70vc as well, wonderful lens.
I go back and forth with 50mm and 24-70. You literally cant go wrong with a 24-70, does everything well.
I go through many phases where I shoot 50 primarily, then 24-70 primarily. If I had to pick one, my brain would tell me 24-70, however, I have a lot of heart for a 50. For travel, 24-70 historically has made more impacting photos, since I'm primarily a scenic shooter.
this current moment, I feel like giving up on 50, even though I have some wonderful 50's, FD 50 1.2L, zeiss 55 F1.8, nikon 50mm F1.2...... Unfortunately, the 24-70 I shoot with is an F4 variety, however to offset it, I also carry a fast 100mm prime. I would like to get back shooting with a 24-70 F2.8 again, but I'll settle for F4 for now.
for lowlight, the F1.4 wins out for sure, however F2.8 is quite feasible, especially with a good lowlight body. As background blur goes for portraits, I'de say 70mm F2.8 beats out the look of 35mm F1.4. That is strictly my opinion of course. I favor longer focal lengths heavily for portraits. I would love a 600g 24-70F2.8 for the sony system.
so to recap, if I had only enough to own one, it would probably be the 24-70, but I really hate having to make those choices so I'll own both fast prime and zoom for now
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Sony A7siii/A7iv/ZV-1 - FE 24/1.4 - SY 24/2.8 - FE 35/2.8 - FE 50/1.8 - FE 85/1.8 - F 600/5.6 - CZ 100-300 - Tamron 17-28/2.8 - 28-75/2.8 - 28-200 RXD
Panasonic GH6 - Laowa 7.5/2 - PL 15/1.7 - P 42.5/1.8 - OM 75/1.8 - PL 10-25/1.7 - P 12-32 - P 14-140