@Ironhead841 I doubt Plus system was a big balance issue as people say it is because if anything a lot of people will argue the attachments themselves gave such minor buff at the expense of minor to major downsides that often running no attachments are better,
Only a few special attachments are problematic such as Short barrel that messes with the base ROF on weapons, the suppressors that ALWAYS had issues with either being trash or meta because it's hard to find a good middleground that makes it not worth the penalties or make any other option interesting or fun.
Ammo types I do agree cause issues with balancing, if anything most issues revolve around the base gun, rather that specific attachments unless its Close Combat ammo, which a number of times have been meta or problematic enhancing what was already wrong with a specific gun.