Excalibur and Ragnarok are names from mythology. One is a legendary sword, the other is the name for the end of the world in the Edda.
A Freezer is the thing at the top (or bottom) of your fridge were you keep your ice cream.
I guess I didn't express myself quite well...
Excalibur and Ragnarok are indeed two big things from legends, or mythology, but at the same time they are in a way quite, how do I say it, famous, often mentioned by the people, to the point where they are almost boring how much they are, well, just that.
But at the same time, they will always be some of the symbols of something, as I already said, big.
Fire too is a word that most of us use without much thinking (fire is fire), but when you think about it, it is the name of one of the most important (for humans) chemical processes in the world, not to mention its other roles related to light, warmth, religion, destruction, etc...
There are more than a few fire type Pokemon in Gen 1, and some of them have something fire related in their names, but only one deserves to have the same name as the element it belongs to.
Same for Thunder, and Freezer, the latter most like having that name because Freezer sounds like Furizaa in Japanese, and more similar to Sandaa (Thunder), and Faiyaa (Fire), unlike Aisu (Ice).
Freezer, I believe, isn't actually meant to be the freezer in the kitchen, but simply something which freezes things
Of course, that is only what I think...
For what is worth, in 90s, when Pokemon still weren't THAT popular, and there was 151 of them, it may very well be that authors were simply giving them names randomly.
The gym leader names tend to have the same effect for me as pokemon names, the biggest example being Fantina.
Her name, along with her native language and implied country of origin, differs depending on the language the game is in. Simply calling her Melissa would've never worked in English. Fantina is one of my favorite gym leaders, and her being Kalosian/French is one of the reasons why. Localization made this possible, and I am forever grateful for it.
As for Misty, 'Kasumi' is indeed a wonderful name, but as a native English speaker it feels too majestic for the second gym leader. 'Misty' feels a lot more elementary. I'd go for Kasumi being the name of the 7th or 8th gym leader.
Kasumi is one of the most common names in anime, often used by classic Japanese characters, such as kunoichi; other being Sakura (Daisy), Ayane, Ayame (Violet), Asuka, Homura, etc...
Human characters in original Japanese have, for most part, very common names.