Idiom or proverb to point out half-measures
Solution 1:
It's worth nothing that "half-measures" is indeed an idiom. In particular "no more half-measures" is a typical idiomatic ejaculation.
I'd say "half-assed", which for better or worse is slightly vulgar/aggressive, expresses what you mean, maybe. "Your plan of isolating the child was totally half-assed, dude. What about the dog?" etc. footnote
There are sundry variations like half-cocked, half-baked, etc. (I don't know "which came first", it's an interesting question.)
A related thing I can think of is "You can't be half pregnant!" which is kind of an inverse to the concept presented.
A related thing I can think of is the complex "You're a few cards short of a full deck..."
footnote I was going to say "half-assed" is slang, but what does that even mean any more in the English-speaking world? (A) Maybe 1% of English-speakers can write with a pencil, they spl lk dis, and spoken speech is so bad it's really descended to being a kind of patois, an argot. (B) With the internet, everyone knows everything at all times, so what is slang? Does it just mean "a bit vulgar", IDK.
Solution 2:
A day late and a dollar short
Too late and too feeble to achieve the desired effect. His apology was a day late and a dollar short.
The subject of the idiom did something, but it was inadequate. It originally referred to paying the landlord for the rent not enough money and after when the rent was due.