imo if you don't make the card then either: the word isn't important, or it comes up again, and you finally do make the card. It's not a big deal.
I'm about 10 years on my Anki deck and have reached the same conclusion as you about keeping deck size down. A single card has a huge time investment if you add up the reviews. Even more if it's a bad card and you fail it a lot. As the words you learn get more and more niche, it's important to weigh up whether a card is worth making or keeping. I actively delete cards that make me feel 'meh' when I see them, or that I fail a lot, so I don't lose motivation.
These days I have a policy to just suspend once the interval hits six months, so that deck size has a max cap and can eventually go to zero if adds stop for a long enough period. Long enough to bootstrap niche words and hopefully maintain them through reading.
I'm about 10 years on my Anki deck and have reached the same conclusion as you about keeping deck size down. A single card has a huge time investment if you add up the reviews. Even more if it's a bad card and you fail it a lot. As the words you learn get more and more niche, it's important to weigh up whether a card is worth making or keeping. I actively delete cards that make me feel 'meh' when I see them, or that I fail a lot, so I don't lose motivation.