The potential list of fighters that could go up or down to 165 is so diverse across the board that this would actually create this completely unseen before mixup of the divisions. So many potential new matches which have not been possible before. .
.. in theory
Although some in the MMA world criticize a potential 165 division as simply "a difference of 5 pounds".
We have some actual measureable consistencies to go by. Lets take the linear curve of weight starting at 135 going up. 135, 145, 155, 170, 185, 205, 265. If you take a look at that chain of numbers you might realize that there is in fact a measureable consistency of weight disparity as you go up in divisions. It is a linear curve. What that means is that the divisions as a whole have a foundation of mathematical existence. However, if we include 165 we now have:
We notice that there is now an inconsistency. The only way to resolve it is to either remove 165 or 170. You can not have both. Since removing 170 is absolutely impossible, the only solution is to remove 165. What's better however, is that it doesn't even exist in the first place.