Personally I've worked out for years doing primarily the big 4, and have gotten good results. Occasionally id do assistance work but not usually. The only thing that's noticeable are my arms and back are a little lacking in definition imo, but not severely. Id say you should be fine, especially if you plan to pick it up more accessory work later on.
I also lift on the heavier side of my %ORM for strength though.
I'm not concerned about definition (happy with what I have), more concerned about symmetry and preventing injury. And both the replies on this post made me realize that maybe I'm lifting too heavy (I'm using 5/3/1 for the first two lifts with FSL 5x5 for the others). I will reduce my training max by 10%.
Yea if your goal is to just maintain and or prevent injuries you should not lift in a 5 rep range (or lower). It is way higher chances to injury when lifting heaver weight compared to more reps with lighter weight (not saying it should be easy or light weight). But it all comes down to what works for you.