The Amiga had good DTP software and hardware at the time. I used them for large format printing. They were initially faster and much cheaper than the Apple solutions.
Large format printing from an Amiga? Surely that is a niche in a niche.
The only pro non Apple DTP people I encountered in that era were Germans with DA's products on Ataris (famously kicked off by an ill considered bet with a Mac owner), and various more workstation or custom hardware type things such as using the Quantel Paintbox for print work, and the odd unix people doing more tech publishing work.
The other thing was Apple became so sticky in part because so many people leveraged Quark Xtensions to a possibly misguided degree, and these proved very non portable. Whole catalogues and directories were being laid out that way.
Once the Quadra’s came out it was all over.