We had a similar issue with Philo on our original Fire Stick that cleared up with a newer one. However, over the past six months, that newer Fire Stick came down with a bad case of not wanting to reliably connect with the router even when I moved it to be right on top of the router while our original Roku happily connected. At that point, I went with a newer Roku to replace the Fire Stick and haven’t had any connection issues.
Maybe it’s a matter of doing what you do and keep updating the Fire Stick. I’ve also found what you found that dipping under a GB of free space on the Fire Stick is pretty much the ticket to poor performance. None of this is prohibitive to do, but I haven’t had the same issues with either Roku.
Yes, we have had every major type of media streaming device and they have aledl work about the same for us... it largely gets back to what you are used to. We have kind of settled on the Fire TVs largely because we subscribe to Prime and they have some programming advantages when you do that. My parents are in their mid 80s and a bit on the technologically challenged side. They use the a couple of 4k Fire Sticks with a great line up of channels on Sling and have been just as happy as when they were using a Comcast cable TV box.
I have a couple of old HP Elite 8300 Ultra Slim Desktop Computers that I have hooked to both of the TVs that we use the most. I use them with a wireless keyboard and mouse or a trackpad that is built into one of the keyboards. They are about the size of a DVD PLayer and even though they have 3rd generation Intel processors they are more powerful than the current tiny Windows 10 mini PCs. We still use the Fire TVs because of their convenience, but whenever we want to record something we use the HPs with a media recording program called Audials 2021 that is currently $19.95. We have been using the constantly evolving Audials program for over ten years.