Why add 50 points to Mega Reuniclus’ Speed when it automatically sets up Trick Room with Speed Swap anyway? Those 50 points would be more useful on literally any other stat. Also, lowering its Defense, even though it was only by 10 points, doesn’t do it any favours since those 10 points aren’t benefiting it in any other stat.
Why cut down Mega Magcargo’s Defense by 110 points if you’re only going to put 20 of those extra points into its other stats? Sacrificing its Rock typing and so much of its durability gave it no benefits beyond Vaporisation (which, unlike Speed Swap, has nothing to do with its stats) despite Mega Evolution granting it a massive total of 210 stat points it could be using.