it is true that strength is not always the vital goal of bb.
But, as some suggest, whatever you do, whether light and strict or heavy and slow or even heavy and explosive, the poundages should go up over time to indicate greater muscle capacity as demonstrated by higher poundages. To me, this is a good guideline for bb's, no matter which way they train.
Having said that, however, a bb could stay on 30kg over time for barbell curls, but just do the movement stricter and stricter. Gary Lewer, a NABBA Mr World, did this.
In contrast, sonny schmidt trained pretty heavy, yet could only do a 166kg bench press, despite coming 6th in Mr Olympia. Saw him do a 276kg back squat, strict as (Olympic style but controlled on way down).