I do believe you are in the wrong putting planters their, but also the SM should apply the rules equally to everyone, and not selectively.
I’d be inclined to photo the offending balconies stating that SM need to take action within 7 days, or you will resume putting your planters back outside.
Bear in mind generally the SM dosn’t make the decision the EC or OC do as the SM is really a Strata Administrator.
If you do get issued with a NTC your photos of others being allowed to ignore the rule might count on your behalf. I’m not sure if they can apply NTC selectively and get away with it.