Running Fedora 26 in a live environment almost feels like native speed to me, but when I install the OS to a thumb drive and boot into it, everything takes forever to startup. Once things start they're generally much faster but it's practically unusable.
Is this considered normal?
It has to do with how they operate.
For a regular installation to a flash drive, you're limited by USB bandwidth, so unless you have a good USB 3.0 device, you're stuck at about 20MB/s (which is equivalent to traditional hard drives from around the late 90's). All changes get written to the device too, so you are sharing that USB bandwidth for reads and writes.
A Live system however operates somewhat differently. At its core, a Live system consists of a base system image (usually a SquashFS image, as it's good for space efficiency) and a overlay mount on top of that to intercept changes and keep them in RAM. There are two specific ways this is handled:
In the first case, you can actually run faster than native speed (because you never access anything slower than RAM), but your startup takes a long time (because you're copying hundreds of MB of data into RAM. In the second case, you're not going to be quite as fast as native speed, but because you never write anything to the falsh drive, you also almost never drop data from the cache, and therefore are running reasonably fast too.
