I'm wondering why it hasn't been mentioned before, but I tested a bunch of different svg->pdf converters and found that the best one is Headless Chrome. It produces the most precise results for me. Before switching to Chrome, I was trying to fight with Inkscape bugs, but many of them are too serious and I can't do much about it (transparency bugs, wrong fonts, etc).
chrome --headless --disable-gpu --print-to-pdf="output.pdf" "input.svg"
It needs tweaks to make custom PDF size, but I was able to set custom size after some googling and playing with CSS and SVG attributes (check out this answer on stackoverflow)
