If that is your world view of tank riders, then limit yourself to the versions with SMG only, then. Your choice.
Of course, the Russians were just like any other army - and experienced troops would "aquire" non-establishment weapons, like the mass use of captured panzerfausts.
Since I have actually served in an army unit, I place very little value on any "official" TO&E chart. However, some "chartered accountant" type wargamers bow down and worship at the altar of the TO&E chart. Hint - the things are a guide to what some bureaucrats thought should apply, and not to the reality of actual units, especially those in combat.
Now, of course, you could always enter "soviet tank rider LMG" into the well-known search engine called "google" and get results like
Kursk
where an SMG company is shown to have 9 LMG, which is 3 per platoon, and with 3 sections that is 1 per section. Which is, funnily enough - what we provide as one of the alternatives.
You have the Mobhack editor, so you can make your own OOBS to fit your particular views, should you feel the need. If you do not like the sections with LMG, do not buy them, and if you are obsessed by a Soviet AI using them against you and swinging the entire battle because 10 elements of 200 or so have these wonder-waffen, then by all means, use Mobhack (its not hard) - and give them an X3 code. Mobhack allows you to have it your way.
Andy