Yes, shinies are supposed to be rare. If you aren't using the tome of want to get shinies, you're throwing. I would argue if you want a specific nether weapon, court of blade might be a better farm because it progresses the tome of want super fast. And you can get shiny/adept/shiny adept court weapons too. I say this as someone who had the tome of want on adamantite ever since the start of the season, I only got the roll I wanted on the second week of act 3 (max range slice + reciprocity). The shiny system is fine currently. You get triple perks.