Is legends theme team still the best?
Of the theme teams it probably is. Though for some positions like the oline you may want the ultimate legends position group chem more than legends chem boost.
I think if you are less close to 99OVR, Legends Theme Team, or really any Theme Team is more relevant. This is my first year playing MUT, and it took me quite a while to even realize that there were bonuses, etc. for being a Theme Team. I picked Legends Theme as it was the easiest one to level up more quickly. I am a 98 OVR now, and with the Super Bowl Strategy card, a good part of my team is 99 OVR, and while I maintain at least 40/40, I don't think those bonuses are contributing as much as they used to to my OVR.
https://www.mut.gg/23/lineup-builder/ac6de947-2e7c-4918-bb4a-f083b39d4fc1/
My Steelers TT has been great for me