Well I am sure there can be work around's for the issues, after all, the weapon on the back is not the problem per se, but the slow switch between rifle to side arm for defense purposes, and if the speed difference is a fraction of 1/8, it is still that 1/8 that could get us killed, op save us. Speeding the animation up though would work, but could look very wrong and out of place, and at the same time would still feel like it can be done faster by dropping the rifle to chest.
only thing I can think of at this point, is perhaps a dedicated hot key for fast switching at least in terms of self defence, and not to be used as default for swapping weapons.
This can work in the sense that it is faster to switch and draw your sidearm but may have to have have a negative impact, in order not to get hurt or damage weapon, the following can be applied:
orrr alternatively since this is animation related:
alter the animation, so by default switching to sidearm will drop the rifle to chest, however if you are sprinting and going prone to hit the dirt, the prone animation is altered if you have a sidearm equipped and rifle to chest, animation will then be to dive down on your left hip side, and swing the weapon towards your back as you hit the ground, then roll flat on your stomach.
And then here is something I would suggest will work too, not so sure how anal other players would be about this.
Since there are no animations for opening and closing doors on buildings or vehicles, or even mounting, or jumping off roofs and knee high ledges, everything seems to be magical and leave room for the imagination to complete. Why must there specifically be a very detailed (and annoying) animation for switching weapons? Why not just cut the animation and focus on the time it takes to really switch the weapon by an average trained soldier, since that really is what matters here, and then have the weapon magically appear on the players back, or drop to chest, but when you go prone, have the weapon magically appear on the back shoulder?