At level 21, Eagle still has an impressive stun rate (95%). Additionally the number of attacks per minute improves at an extremely slow rate after level 21, and adding 9 points into a skill for 4% more stun is a waste to some. Leaving Eagle at level 21 doesn't take advantage of its full potential, but it's still a decent enough level to carry you into 4th job, where your Freezer takes over the job on Maplestory.
During 3rd job, Eagle is the only passive immobilizer a Sniper has access to. By using Golden Eagle, a Sniper can spam Strafe on a target without worrying about it attacking back, because it will be stunned. Without using Eagle, the Sniper would lower damage dealt by having to use Blizzard to keep it immobilized. After third job however, Eagle is almost entirely replaced by Freezer, which immobilizes mob targets. During 4th job, Eagle would only be used again Ice-Based targets who cannot be frozen. By either maxing Eagle or leaving it at level( maple story mesos ) 29, you can maximize its capabilities.
Thrust allows one to maximize speed, without sacrificing damage. With a high enough level(Maplestory powerleveling) of Thrust, an Archer can achieve maxed speed without relying on Haste, or Speed Equips. More speed allows you to move from target to target quicker, and still be ready for combat at any time, unlike using a Mount. Thrust should be at a level where your equips and any other boosts (Pet or Pills) will give you the desired speed you want or as close to maximum speed as possible. Please note that after level 10, points in Thrust are less effective than the previous points.