This is an auto-attack Yi build, not a crit focused one. Alpha Strike is mainly a utility ability. You put the three points into it early because your E is weak until you have a solid attack speed core. When your Q starts to fall off, you stop maxing it and start maxing your E, which only gets better late game. You say that you'd be behind the enemy champ because they're doing standard maxing, but you don't get any bonuses by putting 5 points into an ability. Leveling an ability to level 5 gives you the same increase that leveling it to level 2 did. So you won't be behind them, because your Q will still deal damage when you start maxing your E. Also, even with a more traditional maxing order, my E would only be maxed one level sooner and I'd have an even weaker laning phase than Yi already has.