In my opinion to improve your jiu jitsu you need to train more jiu jitsu.
I can se just a few cases in which I think that a parallel train could be indicated for beginners in order to drsticaly improve its game.
If you are a sedentary person, overweight or underweight person. The train should be focused on strengthening, in order to avoid injuries.
If your strength and conditioning are ok, you will evolve much faster, if you focus on training jiu jitsu. (GI and no GI).
Disclaimer: I'm not telling you not to do a parallel strength and conditioning workout. I'am just saing that in my opinion if you are a beginner, I believe that if you force your energy just in jiu jitsu it will help you evolve much faster.
In practice: if your strength and conditioning are ok, it is better to choose to train BJJ 5 times a week than just 3 in exchange for 2 strength and conditioning sections.
When is strength and conditioning training welcome?: Im my opinion if you are up to purple belt and you’re a competitor.
To finish, some quotes:
Carson gracie trainer of great BJJ fighters
used to say: If you want conditioning for BJJ then roll with all of your training buddies in every session .
Victor Doria a great BJJ champion (actually living in the USA) usually says:
if you want to become strong in BJJ then you have to do strength during training.
(In a technical way)