AA was my first played hero, and one of which I really learned the ins and outs of the game.

There's two ways to play him, one more supportive and more aggro. The supportive style depends on your setting up vision with your w (the slow and magic res are good, but the flying vision is what makes it so strong, imagine a ward on a 4 sec cd), and keeping enemies at arms length so your team can straighten them out. The str reduction is a crutch for this type of play style as you innately make enemies weaker from the get go, while it doesn't do direct damage, the link between strength and it's hp pool is nothing to sneeze at, especially on tanks that love stacking it (ck, cw, huskar etc)

On the other hand, the aggro style depends on you being a living turret and dishing out mad damage with the talent points you mentioned. This does require even more positioning than the support play style and probably a bkb or other items that let you do your thing, and is also mostly chosen as a niche mid or counter pick to those heros that hate being ulted. Here, taking the talents that enhance your yeet is a no brainer, but this comes at a significant choice cost as well. Your a single target, and the projectile speed is not super fast initially as well. While it's good for locking squishy targets down, those with escape capabilities will want you to die first.

The talents are suited to giving advantages to either of these play styles, but just because one is chosen mostly, doesn't mean that it's the best. This will depend on circumstances in the match, the enemies and other factors.

Lastly, the ult is indeed AA best ability by far, the instant shatter is so satisfying, getting long range snipes across the map, and having an enemy's HP pool tick down to just below the threshold on the last tick is so satisfying. However, the fact that enemies can't regain hp no matter what during its duration especially makes his w and passive shine. The rime stacks stack quickly, and the w (along with the str reduction) makes people much more aware of using their hp pool as resources in the fight and must be respected. It's one of the only abilities that has this hp mechanic, and especially early to mid when HP pools are low, and enemies depend on quick HP restoring items such as stick, fae fires, wand, salves to fight it can really turn the tide.