iOS Excel is pretty awful. If you’re just viewing it’s ok as long as there are locked column labels so you can scroll and not lose your place. But editing or formulas forget it. Everything else I can do on my iPad without headache. I manage cloud in AWS & Azure so being on the go and the portability of an LTE equipped tablet that lasts all day is great compared to lugging around a bag with a laptop, charger, pen, and paper. iPad is all in one for me.Unfortunately I am both team lead of Software Development team (former Software Developer) and I do need to use sometimes big Excel sheets so I kind of fit your example . Nevertheless I am actually quite curious for the people that can do all of their work on an iPad. Not because I don't believe them. I am just interested in their workflow because I never know if it is something I don't know or it is just also about a preference I don't lean towards.
So contrary on your belief I would not tell you that your opinion is wrong. I actually love the way the iPad Pro 11 looks like but I am worried that iOS cannot offer me what I need fully and then I would not want to pay such price for a secondary device. That being said I would not say completely No for the years to come. It is a definite NO but for now and given my usage, workflow and expectations.
I tried the Surface for awhile and the kickstand was uncomfortable to use in the lap while trying to type or use the touchpad mouse, the pen was useless and couldn’t even function as a mouse, it’s writing recognition in Word was bad really bad, and the onscreen keyboard isn’t very fluid, and touch inputs while they work it’s just not a great experience in Windows. As a light laptop with a full desktop OS it’s good enough as long as you have a table to use the flimsy keyboard on.
The iPad I can hold in one arm like a notepad and do everything I need to with the other. Windows 10 just doesn’t function well that way, it tries too. But that’s just not it’s OS design it feels very tacked on as far as capabilities go. Both have their strengths and weaknesses. It all boils down to what you need to do and using the right tool for the job. For instance I couldn’t imagine making a pivot table from a Microsoft recon file with iOS Excel. But for me that is all I need desktop version of Excel for and that’s once a month.
General purpose iPad all the way.
Workhorse needs or programming you need a desktop class OS in my opinion.