This discussion can go in any number of directions.
The Librem 5, when I have it, will be able to do some things that my current desktop computer cannot (e.g. touch screen) and actually has more cores than my current desktop computer (4 v. 2) - but for sure it won’t be able to do some things as fast (e.g. compute intensive stuff - I posted some benchmarks based on the Pi a while back Raspberry pi software information - #30 by kieran)
The main thing is that one day it will be … in my pocket - and I’m confident that my current desktop computer can’t do that. 
I didn’t read all the replies in this topic but it is also fair to point out that, where the Librem 5 is not itself up to the job, it can be an access device for a computer that is up to the job. Remote in to your high end computer to kick off your Computational Fluid Dynamics job or your Quantum Modelling, and display and interact with the results on your Librem 5 when the results are available, anywhere anytime.