It's not just about being able to start the application, but to actually use it: with an arm you run into performance limits pretty fast, whether you do many realtime-effects in a daw, lots of I/O because of recording many high-quality sources at once, encoding/decoding, or high-quality cpu-demanding image calculations with photoshop.
I'm using a 6-core AMD64 for a DAW and it's trivial to get it to it's limits whereas photoshop is *always* too slow, on any system I've tried
For only moving and resizing an image every now and then and other office-like tasks I agree ARM quadcores are nearly usable, but definitely not for anything more demanding.
I get amd64 computers for free these days. You can also buy them used on ebay, they are dirt-cheap. Thinkpad T61 is <150 Euros nowadays and it comes with case, screen, mouse and keyboard included
35 Dollars + case + keyboard + mouse + screen I think is approaching the price of a proper Thinkpad T61, and it still doesn't give you the same mobility. Oh, and the thinkpad has a UPS included (the battery)
The reason I brought up the cubi is because you called your alternative a rpi competitor. As rpi by no means excels with performance or stability, but if at all then with usable video decoding under linux I wanted to present you the only usable ARM competitor in that domain that I know of. There are also some nice MIPS systems out there btw, if I had a bit more time I would tinker with those, too.