Unlike development, UI design is very subjective because everyone knows and understands colours, fonts, styles. This gives us the confidence to be vocal in our preference.
Founders, Marketers, Product Owners — we all have an opinion on how something can and should look, and this opinion can become quite impassioned when it’s your own product; your heart and soul. From my experience, the key to building a product with great UI design is in the involved parties providing their design review feedback based purely on their requirements (brand, functionality etc.) rather than their opinion, and empowering the designer to have the creative liberty to bring those requirements to fruition in the way only they are qualified to do.
I think you do need a multitude of opinions and people to build a solid, comprehensive product that has been considered from all aspects, but this only really works when each department head / lead person is both trusted and empowered to do the role they were hired to do, rather than what they’re being instructed to do by management.