I agree about confusing MMR but with guns most games let you know damage, range, fire rate, accuracy/range, damage fall off, armor piercing, etc in a chart type format.  Like how much more damage does the Hornet do than the Smerch.  I have no idea.

I would say they were going for something more along the lines of Overwatch than Warframe. I don't think your decision making process in which guns to use is meant to be based on macro stats. I believe they want you to choose a weapon based on it's abilities, and then adjust to that play style while finding a way to make it fit in tandem with the CQC melee system. H.I.V.E.'s starting weapon, for instance, makes it easy to ensure you are infecting specific enemies, but the RACEME offers a longer range for her life drain. The trade off being it is a bit harder to use, and has a lower clip capacity. Her PLAGUE rifle, on the other hand, can penetrate walls and also empty a full clip in close combat to ensure infection. If I use PLAGUE on Hanging By A Thread, for instance, I can infect an antag through the floor if he/she is on the second level, thereby assisting a team mate who may be in the middle of an encounter with them.

I don't meant to sound condescending, but again, I think Mercury Steam designed the weapons around their function first and foremost. Sure you can bring up certain stats like crit damage, damage done to players or AI enemies, but in general those percentages act more like indicators to me about how I can slightly modify a specific weapon's usefulness in certain situations.

I don't think this is meant to be a game about math, where my numbers beat your numbers, but unfortunately uneven matchmaking, where a purple tier 1 antag can go against much lower levels, can make it seem that way.