Riven main checking in.
1. Riven has sustain, her early hp5 and shield make her one of the highest sustainers in top lane early, and the fact she naturally itemizes lifesteal makes her one of the highest sustainers in top lane late. To say she has no sustain is misleading.
2. The reason she is not as strong as other bruisers isn't all because she does 100% physical damage with no natural shred, but she's just not as effective as an Irelia flying into the enemy team and instantly bursting the enemy AD, a jax doing the same while stunning the enemy peelers and proceeding to kill everyone else, or an olaf running into the enemy Ashe/Janna/Turret and coming out with 80% of his HP and a double kill to his name. Other bruisers just do their job better, and more consistently.
3. I personally max W, I'm not alone here. If you play Riven you'll find yourself using Q for mobility most of the time. Riven has early power so increasing your trading isn't as effective as making trades happen more. The fact you can run into the enemy and hit them with your 3rd Q>Ignite>AA>W>AA>AA>Wind Slash for a kill is what makes Riven special, not that she can trade with someone who decided to trade with the champion whose power is in the early game.. Not to mention it lowers the cooldown on W. I have experimented with Q on riven enough (ok, I've experimented with everything on riven) and I personally don't like it.
4. On your comment about what you max is matchup dependent- against rumble you go dorans and first blood his yordle butt. If you don't do that, you max W, push him to tower early, and outroam him all game. Maxing Q is something you'd do if you wanted to actually trade with him, but why trade with a Rumble? What can happen in a rumble matchup and the solutions: 1. You succesfully FB him, lane is now secured and you should max W to beat him up further. 2. You don't FB him, you push him to tower and can outroam him, maxing W to roam. 3. You get camped by jungler hard, or FBed by him due to severe misplay on your part, or in general just mess up the lane, preventing roam. Maxing W will give you the best chance at surviving, allowing for waveclear when needed along with CDR for hitting them back when they harass under tower/gank.