It's not a weird phrase to some, just as many folks have used terms like load-bearing for a long time. People are defending it because it reads fine to them, just as some are attacking it because it's not their preferred language, it causes them confusion, or they're just triggered and seething.

LLMs have made people so sensitive to language that I fear we're going to throw the baby out with the bath water. The models obviously need work, but they're also a great opportunity to expand our own vocabulary and grammar. It would be a shame if we deny some of the finer points of language in favor of Grug-speak to appease the lowest common denominator.

"Frontier" may be jargon, but by this point it's definitely established AI jargon. In the context of AI, it's clear what it means. It means the same thing as the last billion times you heard someone mention "frontier models".