We can call it a Russian BTG or we can call it a US Combined Arms Battalion. It is the same construct employed differently. (Actually it isn't the same construct as somebody will be along to tell us shortly - the BTG includes Gunners, Engineers, Loggies and a bunch more bits and pieces while the Combined Arms Battalion is an Infantry - Armo(u)r organization). Our doctrine calls for mix-n-match forces with various types of command and control depending on the situation, so I don't see a problem with sub-units being raised and combined in "permanent" units. Those "permanent" units may only be notional, garrison, training units that are ripped apart for deployment but they would form a cohesive unit for immediate use.
As to the Reg Lt Col and Majors and Reserve Captains I admit to letting my historical biases influence this. Traditionally the field grade officers are Colonels, Lt Cols and Majors. You can tell them apart because they wear the Crown. Captains and lower only have Pips. The Field Grade officers are the Colonel, his Lieutenant and his senior sergeant, or sergeant Major. Just like the Captain-General, has his Lieutenant General and his senior sergeant Major General. 'Pologies, favourite digression of mine.
More to the point the Field Officers gained their authority directly from the Crown or State. The Captain, historically again, raised his company, be it a company of fusiliers or a ships company, from the local community, and then was required to regiment them under the direction of the people considered to be Field Officers.
To my way of thinking this still works for a Canadian reserve system. A Captain can recruit, raise and train a body of soldiers that can put their clothes on right, salute the right people, march, run, shoot, read a map, communicate, dig a hole and perform first aid. She could even be expected to get her sections acting in a coherent manner. But I have not been convinced that there are enough hours in the year available to the Reserves to make even companies and company officers proficient in combined arms operations.
Consequently I would look to the Regs to supply the Field Grade officers and their Warrant Officers to conduct higher level training and administration.
Having said that, the Regs would have to want to do the job and the Reserves would have to want them to do it.