In Geospatial Community there is always a divide on which tools are better and what tools should I learn to excel in my career as Geospatial Professional. Let me tell you after working for around 6 years in the geospatial domain there is no single winner out of the two.
Hate for ArcGIS
I have hated ArcGIS to the core since my college days and many people will agree with me on this.
"Why is it slow?"
"Why do I have to use two separate tools to complete one simple task?"
"Why do I need so much computing power on my system?"
"Why is there no clear support online for ArcGIS Python Scripting?"
And many more issues. There are Reddit posts on ESRI sucks and I hate ArcGIS Pro.
Opensource for the win
I was an open-source geospatial fanatic, if you can do it using code why spend on an expensive tool? I initially worked in startups and for obvious reasons we did not have ArcGIS. All my work was in Python, PostGIS, WebGIS, and QGIS. The whole ecosystem was built from scratch and the flexibility it gives you to automate your process.
A mix of Both
When I moved to a bigger consultancy firm, open-source GIS did not help me very much. We were using the whole of ArcGIS ecosystems that had almost all the ArcGIS licenses which are available from Network Analyst to Online. I clearly understood the use of ArcGIS then, you could deliver a project in a matter of 2-3 days using ArcGIS with 1 or 2 iterations, but this is not true when using open-source GIS. Although certain clients did need products around GIS analysis where we used open-source GIS and delivered base products for certain repetitive analyses which they needed.
Conclusion
ArcGIS is good for projects where a client needs a quick turnaround and need to make some important business decision. Open-source GIS is good for building products that we can scale up by using other services available out there. Financial is another way to decide which tools to choose from and manage your ROI. For any person looking to grow their career in the geospatial domain, try to grasp the knowledge of both.
If someone gave me a task today to perform a drive time analysis for a set of 50 locations of my hotels and include certain other POIs along with it, I would want my ArcGIS license back. But if the same tasks are required to be done regularly every month I would create a product around it and add more KPIs to it.