does the dup
completion-item option work for that? it should at least dedup items from the same source, which should work as it's all the luasnip source(?)
https://github.com/hrsh7th/nvim-cmp/issues/511
https://github.com/hrsh7th/nvim-cmp/blob/main/doc/cmp.txt#L534
https://neovim.io/doc/user/insert.html#complete-functions
it matters in what order the items are loaded in with this: the first one wins
can reommend both