Agency people are usually 'creative' - that's not what makes good marketing.
Rules of brand are: clarity, consistency, authenticity. While branding is only one part of it 'clarity' can be applied everywhere.
I'm looking at data.ai aka app annie right now and I want to wrangle he marketing team it's ridiculous to try to fathom what all their dumb products do - they only use abstractions.
Literally 5 products that 'increase ROI and help you meet OKRs' or whatever, my god man What the F is it, and what does it do? is the question at hand here.
Admittedly, it's not always so easy but focus should be on that.
I've met some very creative ad/marketing people and they're great fun. But they're very much the exception.