If all players require minimal investment in Fight Game Survival Game to be considered viable than such investment should, again, be mandatory.
But all (my) players don't
require such an investment. Again, you can get by with no combat investment. It makes you vulnerable, and it puts the onus on your circle to protect you, but depending on your group dynamics
that can be just fine, especially if your lack of combat investment means you could splurge in other areas that are of greater benefit to the group.
If a section of the game is mandatory to all players, than all players should be given automatic investment in that area so that they do not get eliminated from the game.
No, why? Not everyone gets the spotlight in all scenes, that's fine. You don't get automatic free investment in social influence either. You don't get automatic free investment in
anything, because again this is a group game and you can trust your fellow players to compensate for your lacks. However, you get
cheap investment, such as having easy access to free Excellencies and powerful entry-of-the-line Charms if you just want a quick "basic superhuman competence" suite.
But you don't have to; you can do without.
If your character has spent all his skill points in Decking then he can't do any of the other things the Shadowrun team needs, so the player gets to sit out those portions of the game. Maybe he says "I stay in cover until the other PCs tell me to move" every now and then at the GMs assistance.
Why should we be forcing players into sitting around twiddling their thumbs for hours and hours on end? Why are we giving the illusion of choice in the game system if players require a minimum combat suite? Just give them the combat suite instead of subtracting its ability dots/charm picks/background dots/merits/bonus points from the supposedly 'free' picks.
If I force players to "sit around twiddling their thumbs for hours on hand" then yes, surely I have failed.
Fortunately, I am an experienced GM, and I have at my disposal such tools as "run the Decker's thing in an off-time solo session," "cut things short and move on to a new scene when the present one is taking too much time," or "make the scene compelling enough that the non-involved players still get enjoyment out of watching it." I also don't run with sociopaths, so there's a general understanding among my groups that sometimes your character gets phased off for a little while when a scene mostly focused on the skillset of another part of the group, and that's fine because this comes around in due time.
One of the more popular sections of Gloam City Nights featured a single player acting. It worked out because I can read my table well enough that I was confident they would enjoy just "sitting around" watching Song having an important duel, as well as because they still had the agency to cheat in some fashion or break the rules established in-character if things went wrong, so there was tension even for those not engaged in the action. If this had been set not to work out I would have instead split it off into a different, solo session.