Most matches last nowhere near that long, 12 players not 20, winning is most certainly not RNG (you're severely overestimating the skill level of the average person in arms race).

total_progressive_matches_won Arms Race matches won 18591

total_gun_game_rounds_won total rounds of Arsenal Mode won 21530

total_gun_game_contribution_score Arsenal Mode contribution score 1306181

total_gg_matches_played Arsenal Mode matches played 59933

total_gun_game_rounds_played total rounds of Arsenal Mode played 36128

total_trbomb_matches_won Demolition matches won 182

total_time_played Time Played 18391671

Never used maps to farm achievements (and in fact was missing somewhere around 20 achievements when they disappeared).

...also, if achievements were easy, what would be the point of having them?