Swifties+Alacrity is a serious problem.

Namely, it just adds too much flat MS into the game. Because of how MS works in this game, having so much flat MS in the game being so easily accessible multiplies the value of %MS boosts which are very common. Combining that with the slow resist on swifites and the slow resistance in the resolve tree gives us with a bunch of bruisers that are insanely fast at all times that are also very resistant to slows. It honestly creates an MS arms race where any champion that has Swifites+Alacrity is both uncatchable and inescapable unless you also have them. It's so strong that lots of champions are even rushing Swifites first item because it turns out you don't even need many combat stats when you can simply run away from any unfavorable trade or duel. I'm aware that Swiftes are being nerfed on the PBE but I don't feel like it will be enough; champions really weren't designed to be this consistently fast in combat and slows definitely weren't designed with slow reduction being this ubiquitous.