Proton is the best email service ever existed. Period.

However, its biggest flaw against competitors is that email is the least used tool for collaboration nowadays, and Proton lacks integration with most other tools due to various factors, with the most obvious being its completely different concept for security and data ownership.

So, how can Proton be better than MS Office and GWorkspace?

Here are some ideas that I think can be created (relatively) easily.

1. ProtonOffice - Integrate OnlyOffice in Proton Drive and whitelabel it (they offer this possibility i think. (Or even better- acquire them and rebrand them to ProtonOffice :)) OnlyOffice is the best alternative to MSOffice and the most compatible with it (which is crucial, when a company wants to have a good OSS-based and secure tools but at the same time to keep being "compatible" with the rest of the world that unfortunately uses MSOffice). The tools for Docs, Sheets, Slides, PDF, and Markdown are there. No need to invent the wheel. Integrate them into Proton Drive and offer a real document collaboration suite.
2. ProtonChat - Create a Matrix/Element-based team chat/collaboration service. Matrix is the best service for secure, encrypted chat in the world, but it lacks UX in all possible ways, making it difficult for a small to mid-size team to use it effectively. (the way they offer their services, the way to install and maintain it. It would be more than great to have a Matrix-based chat with Proton UX and Proton hosting out of the box with the Proton Business Suite.
3. Proton Identity + OAuth - this is self-explanatory, the last missing piece of the puzzle to have a complete suite for SMBs that can fully replace O365 and G-Workspace.

These 3 things are crucial for a complete business suite. I have a personal account in Proton myself, and I adore it. However, the lack of true document collaboration and chat is what stops me from migrating my business to Proton, and I am sure that there are many businesses with the same obstacle. The ideas above propose a way to ship them as quickly as possible without compromising the Proton concepts. There will be work, of course, to integrate them properly, but it is still much easier and faster than inventing the wheel from scratch and developing all these tools.