Summoner's Insight is crowding out other Mastery choices

I don't have a problem with the mastery itself per se (as in the cooldown reduction on Summoner Spells is intrinsically OP). The problem is, that you need it, particularly as support, because the opponent will take it. Not having your flash/exhaust for about a minute longer than the enemy leaves you too prone to being all-inned. Particularly in high levels of play, people abuse this if you don't take Summoner's Insight.

As a result, champions that could viably go 12-18-0 like are in essence "forced" to always go 0-18-12. It'd be nice if we could have more options for mastery setups.