If you upgrade the weapons the springfield gets outclassed by several other rifles. Almost all of the rifles are balanced in one respect or another against the others. For instance, the Mosin (fully upgraded) has the best long range killing power and straightest flying bullet but is slow between shots and only holds five rounds. The springfield is slightly less in many regards but shoots a little faster. The KAR98 is close to those two but sacrifices some power for better handling.
If you upgrade the weapons they each end up having their own place in the lineup for however you prefer to play. Some, like the swedish mauser or mannlicher, seem to pale a little compared to other choices, but each has it's own unique feel and is viable.
Reading many of the complaints it is clear that the complainers haven't grasped at the depth involved here. And upgrading the weapons is meant to be a challenge. Forcing the player to perform certain actions challenges them to develop new tactics/gameplay styles. The freedom is that you don't have to do it. The upgrades are not essential, but significant enough that I think they are worth the challenges.
I've tried every gun in the game and all are viable. My usual choices are Mosin for long range pure sniper PVP, KAR98 for mid-to-long range general purpose, Garand/Gewehr for any urban map.