Unreal Engine is kind of garbage, so...ideally no. At least not for anything that demands high framerate/graphical fidelity.
Not well informed enough about Unity to say for it.
Unreal is very capable. Dragon Ball FighterZ is UE4 (and works wonderfully on Switch too), Dragon Quest XI is as well. So is Kingdom Hearts III. And a number of other games.
Both DQ and KH can only hit 30 FPS consistently on consoles to my knowledge. KH's "unlocked" mode often has serious frame dropping problems on standard consoles; Pro and X handle it fine but standard PS4 and XBO have lots of documented issues, and that's with hitting relatively tame resolution standards of 900 and 720p respectively. And the Switch is technically less impressive than either base XBO or PS4.
This isn't to say that it's impossible to make good looking/well performing games with Unreal (Arc did a fantastic job with DBFZ), but all the evidence in the world points to it being a substantial handicap if you're aiming to make games with high resolution output or high framerate. A reasonable point of comparison imo would be looking at Devil May Cry 4, which ran on MT Framework, and going to the DmC: Devil May Cry reboot, which used Unreal. DmC launched in 2013 and had numerous problems with textures popping in/out, could only manage 30 FPS on consoles, and frequently fell below even that on PS3. Conversely, DMC4 ran on MT framework and was locked at 60 FPS with no such texture problems despite launching five years earlier.
One of the big problems is that UE (especially UE4) is very resource hungry, and devs need to put in more effort on optimization to make sure that extra assets aren't going to tank performance. Optimization is important for all games, but especially so for Unreal titles, and it's an extra layer of work/chance for things to go wrong, especially if your system is (relatively) underpowered like the Switch.