I think it’s just a carryover from RTCW. Codewise it would not be necessary to be able to select an SMG as primary to be able to select it as secondary.
Seriously tho, whats the point in going Soldier/Smg. Even if they were to have ‘high base health’. Why not take the risk as a Fops/Medic or Engy with the lower health but makes it up for it with numerous extras. Eg, Artys, Mines and Reviving/Healing.
A soldier could have “extras” too - but if none of these extras would require active use, that would be the point of the soldier - you do NOTHING but moving and fighting with SMG, nades and knife. How about killing x enemies (and no teammates!) in y seconds triggering a somewhat milder and shorter adrenaline effect? Etc. etc. And don’t discount health boni and kevlar wests before thinking it through in your head. Of course the heavy weapons might need some tweaking too. Or what about an undeployed MG42 doing less damage and having recoil, but more accuracy (depending on HW skill too). Bwahahaha… you see, my approach to “modding” is to nudge stuff into the direction I want - but rather way too much than too little (most of all because I’m usually not sure wether what I changed had any effect :P).
Balancing can come later.
Idea: on low health the medic regeneration increases much quicker - headshots would still be a risk, but that would make them even more unkillable. Kinda unrelated: (I just thought "they would survive to drop packs for the team around the corner) -> wouldn’t it be nice if people waiting for medics could crawl slowly? I wouldn’t even care if they would just slide on their backs for the time being haha 
maybe you should switch from ET to CoD ? Or UT ?
[…]
So I say: don’t change anything
Hmmzz…? Consider this a thread that would better fit in the modding forum. There will never be an official gameplay patch. Not all mods will ever share all features. ETmain will always exist, ETPro will (hopefully) stay “the best vanilla ET” - you have nothing to fear. You will never be forced to play anything but the game you’re used to.
But if you think for a second you can stop anyone from modding sillly shit - well, think again 