Certain small details in FSL are more "accurate" than Fenix. There's the obvious point that FSL has both IAE and CFM engines in the base package, and they offer the 319, 321 and SL variants. There is also the problem with the engine's burn performance but in fairness, they have addressed the issue as being an issue with MSFS and are working to get a custom engine model in place.
I've heard from real pilots that the Fenix's climb profile is out of whack, it can nose up 15 degrees with one engine only which is not realistic, but again it's probably due to that inaccurate engine model that they're already working on.
Another thing is the old ADIRS panel on the overhead, which the Fenix has. In the real world, the older IRUs cannot do RNP AR approaches or fly RF legs. For some reason though, the Fenix is able to do both perfectly fine. The newer ADIRS panel you see in the ToLiss A321 NEO or FSLabs is more accurate of a depiction to the real aircraft as of recently. It's an easy fix though, since they just need to change that panel's 3d model to the newer ADIRS panel to properly reflect the version of IRUs they're simulating.
There's still value in Fenix, but it's still not yet "better" than FSLabs at this very moment. Of course, if you value visuals more, then there isn't any reason to choose ToLiss or FSLabs at all.