I love how you automatically insult anyone who disagrees with this idea because whatever their reason is, it's likely not real. That's quite rude.
Wider weapon selections will over-saturate the selection of weapons, making the choice between aircraft much harder. One of the reasons you may pick the F-15E instead of the F-15C, or the Su-33 instead of the Su-35, is because of the weapons it carries. If all of these planes carried all of the same or very similar weapons, that entire reason for choosing one aircraft over another doesn't exist. A lot of the aircraft in the mid-tier fly very similar to each other; we don't need even more similarities between them.