Actually it's best stats are it's HP, Def and SpDef ;3. And it's Special Attack is higher than it's Attack.
Anyway, yeah Tropius is most commonly seen as a wall in Competitive, courtesy of it's DW ability Harvest which gives it a strong chance of continously getting Sitrus berry back, making it an extremely annoying Pokemon to face. Also you don't just train 250 EVs on defense, since you need multiples of 4 to affect the stat :3
Anyway in competitive play, the 'walling' set (In NU) would be a subseed being;
Tropius @ Sitrus Berry
EVs: 252 HP / 252 Def / 4 SpD
~ Leech Seed
~ Air Slash
Leech Seed to cause damage & regain health, substitute + protect to stall, STAB air slash hit's grass types that are immune to leech seed. Sitrus Berry heals you when you get too low, and Harvest gives you a 50% chance of regaining it - and with Protect that means you will probably get it back = more stall.
Ingame it gets outclassed, in higher tiers in competitive it gets outclassed. xD