I think the question regarding carbines is because the updated rules for these weapons have been released (but not for the breacher team blasters)
[url]
https://spikeybits.com/2021/11/gw-reveals-new-genestealer-cults-tau-custodes-rules.html personally I never saw much point in the breacher teams unless they are really close and have support form other units / terrain to prevent them from being charged, otherwise I would just take strike team.
When looking at it at the moment then it would make sense to have the strike team carbine over breachers as the only time the breachers are better is within 10” or in other words within charging distance (assuming flat open surface) and that's still no good in tau.
(when the blaster rules are updates then it will be more of a choice, and the update MUST be a good one or no one will take breachers)
Breacher teams @ inches:
15” Blaster, 2 shots S4 AP0 D1
12” Pistol, 1 shot S5 AP0 D1
10” Blaster, 2 shots S5
AP-1 D1
5” Blaster, 2 shots S6
AP-2 D1
Strike teams @ inches
36” Rifle, 1 shot S5
AP-1 D1
24” Carbine, 2 shots S5 AP0 D1
18” Rifle, 2 shots S5
AP-1 D1
12” Pistol, 1 shot S5 AP0 D1