I own both. I worked as a manufacturing bench jeweler for 7 years; so am quite familiar with use of a Foredom.
I use a Dremel tool a lot, compared to the Foredom. It is portable, light, and extremely handy. The Foredom is more or less fixed in place, heavy, industrial and in general an excellent tool. Both have their place. I'd compare them more as a Ford F-250 4x4 compared to a Chevy Impala. Both quite nice and useful for what they are intended for, but they don't have similar purposes, although their usage can overlap.
I've tried other small corded tools, but always return to the Dremel. I use the higher end corded ones with multi speed and chuck instead of collets so I don't have to change collets to change tool sizes. I have a holder with a couple hundred different tips and tools in it that I use routinely.
The Dremels don't last forever; they're an expendable. I typically replace mine about every 2 years; they burn up eventually if you use them a lot and use them hard. I do both of those things. But, so do all the other small tools. The bigger ones last longer, but they're not handy to use. Dremel has hit the sweet spot balancing size, usability, power and longevity.
When I have industrial level grinding or polishing to do, I use the Foredom. But, I use the Dremel primarily with damascus cutoff wheels to cut hardened steel, shorten drill bits, cut off nails, grind small items, and polish inside small things where you can't get to with a buffer.