Putting a carbine in the hands of an SRO on a daily basis helps to ensure precision shot placement. It certainly trumps a pistol or a carbine locked in the cruiser.
I understand that many communities do not fund their agency's training and equipment adequately. Some because they just don't put a premium on those skills and just fund enough for day-to-day operations. The fact is that MOST officers will never fire their weapons in anger in a 25-year career. Officers working narcotics or fugitive task forces, SWAT teams, protection details, etc., in general get a lot of firearms training. Some agencies are fortunate enough to have a robust training program with adequate budgets to sustain ongoing programs. That depends, of course on community expectations and leadership. There are some officers who are outstanding in their work performance but struggle throughout their careers with firearms training. We will never get perfection but strive to improve wherever possible.
Some communities will not fund adequately because they don't want to promote "those racist trigger-happy warrior cops" and see the police as undesirable, or at best a necessary evil. The irony in this is that officers who are highly trained in the use of force are confident in their abilities and far less likely to use unreasonable or unnecessary force. Another irony is communities wanting to eliminate armored military vehicles and other protective equipment which can enable officers to enter a kill zone under fire. If your community fails to support and fund adequate training and equipment, shame on them.
Sheriff Ivey in Brevard is a professional who has a bias for training. That department is accredited for LE and for Corrections, which means they have a wide range of professional standards they must adhere to, including training standards. I can tell you that department is dead serious about law enforcement. Carbines on SRO's are a good idea.
Ask your local elected officials if your department is accredited, and if not, why not? Ask how much range time and ammunition those officers are allocated. You can't correct training shortcomings until you expose them and start talking about it.
Here is something to consider. Florida's Guardian program provides in law for armed guardians in schools. They could be existing staff, or people just hired for the purpose of being guardians. They must undergo 120 hours of training provided by the sheriff on the range, to include precision marksmanship training. I am told that fewer than 50% who attend the training fail in marksmanship. SRO's you can bet are expected to attain the same level of proficiency. It is only when your elected officials place that kind of emphasis on the training that you will get the competencies you are looking for.