Except Salamence, Metagross, and Charizard do need Mega evolutions because right now they're in the low tiers without their Megas. Charizard had been suffering the most, despite being one of the most popular Pokemon, and since the beginning of Gen 6, Salamence and Metagross dropped out of OU when Fairies were introduced and Steel lost their Ghost and Dark resistances.
I can't believe you guys are all for this. The days of cross-gen evolutions are over (unless you're Eevee), as Mega Evolution provides a solution to giving older Pokemon a new purpose to battle in the high tiers without being criticized for their appearance, which was a major criticism for cross-gen evos (e.g. Probopass, Rhyperior, etc.). No megas in Sun and Moon would be extremely disappointing for those who were hoping for new Mega Evolutions of other older Pokemon who were waiting in line to get one.