Question A slangy dialogue meaning 「ふたりとも、使いどころさえ間違わんかったら有能なんやけどなぁ……」

[zeroh4nter]

While reading i met a character using slangy Japanese, hope someone could help me understand correctly what did this mean o/
Story context: The generals are holding a castle against the enemy's siege. Instead of stay inside and defense the castle, they headed out to intercept enemy's attack first. Though other 3 friends of general 呂布/恋殿 told her don't attack too far in to enemy's lines, she still impatient and start to charge forward with another general.

呂布「……うざったい」

陳宮「なんと、恋殿まで突撃を！？」

賈駆「……あの子もああ見えて、結構短気だからね」

張遼「ふたりとも、使いどころさえ間違わんかったら有能なんやけどなぁ……」

 

[Mikawa Ossan]

Would it help to write it like this?
ふたりとも、使いどころさえ間違わなかったら有能なんだけどねぇ…

 

[zeroh4nter]

Would it help to write it like this?
ふたりとも、使いどころさえ間違わなかったら有能なんだけどねぇ…

If both of them (the generals who go to far into enemy's formation) know when/how? to use their strength correctly? ,then they can be competent generals ?

If my understand was wrong feel free to correct (the author often omits subjects in his writing so it's hard for me to know who's talking about who ==' .

 

[Mikawa Ossan]

I get the feeling that 張遼 is referring to their (short) tempers (短気) since it's a trait the two seem to hold in common. In other words, they're too brash. Keep in mind that I'm not a native speaker. I just lived in Japan for a number of years and used to know the language fairly well.

 

[NANGI]

Konnichiwa zeroh4nter-san!

Main text
"ふたりとも、使いどころさえ間違わんかったら有能なんやけどなぁ……"

Translation.
"If you can assign them missions well, they will do great..."
or
"If you assign them tasks that match their abilities, they will perform optimally..."

It would normally be followed by the following sentences.
"But if you don't assign them missions well, they won't reach their full potential".
or
"But if you don't assign them missions well, they will not perform as expected."


使いどころ means "duties appropriate to ability".

間違わんかったら means "don't make a mistake".
(間違えなければ)


In this case, the wrong mission was given, causing it to go out of control.

NANGI