Providing Haste wont matter in every situation but synergizes well with double spell decks, casting a low-cost creature, then pumping it with Rune of Speed while taking advantage of casting a second spell
Boros Energy is the most popular Modern deck at the moment, and by a decent margin, seeing twice as much play as any other individual archetype in the format

Table of Contents show The Deck City of Brass | Illustration by Mark Tedin Commander (1) Planeswalkers (3) Chandra, Torch of Defiance Narset, Parter of Veils Ral, Storm Conduit Creatures (21) Archmage Emeritus Balmor, Battlemage Captain Ardent Elementalist Thermo-Alchemist Murmuring Mystic Young Pyromancer Archaeomancer Talrand, Sky Summoner Dualcaster Mage Firebrand Archer Pink Horror Third Path Iconoclast Harmonic Prodigy Electrostatic Field Niv-Mizzet, Parun Storm-Kiln Artist Deekah, Fractal Theorist Poppet Stitcher Displacer Kitten Snapcaster Mage Spellseeker Instants (17) Temur Battle Rage Snap Lightning Bolt Counterflux Counterspell Chaos Warp Reverberate Ghostly Flicker Expansion // Explosion Delay Remand Essence Flux Prismari Command Arcane Denial Pyroblast Chain of Vapor Mystical Tutor Sorceries (12) Chain Lightning Preordain Overmaster Baral's Expertise Ponder Expressive Iteration Vandalblast Heat Shimmer Windfall Gamble Crackle with Power Time Warp Enchantment (1) Artifacts (8) Mind Stone Izzet Signet Talisman of Creativity Arcane Signet Fellwar Stone Sol Ring Gilded Lotus Thought Vessel Lands (37) Command Tower Shivan Reef Sulfur Falls Cascade Bluffs Fabled Passage Riverglide Pathway Reflecting Pool Training Center City of Brass Stormcarved Coast Steam Vents Spirebluff Canal Scalding Tarn Mountain x11 Prismatic Vista Island x12 This is a spellslinger deck through and through

Times were different, things were new, designing a game is hard, and attention to detail is a skill that not everyone possesses
It doesn't matter what happens to the creatures in response
Vigliance is a static ability seen on the example card pictured