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Pokemon need moves to function. Limiting the moves that are available directly limits a Pokemon's ability to be used in battle.
Items exist to assist a Pokemon, but cannot replace the moves as a means to deal damage.
Limiting the items that a team can use forces the player to adopt different team members that fill different roles from each other, adding a depth of strategy to the teambuilding for what boost a Pokemon can get.
It's already bad enough that a VGC team can hypothetically trick a choice item on 3/4 of the members. Imagine how bad that would be if it were 6/6 of the team.
Move clause is a retarded idea because rather than present a powerup that can easily be altered, you're talking about moves like Protect that fundamentally don't harm teambuilding creativity to the extent of LO everything on the team.
tl;dr: retards just butthurt because they can't HO LO their smogbirds and gaychomp.