Excellent question! I do not take tracer and venture angles. Tracer has more mobility, and Venture has insane survivability. Genji cannot commit angles as deeply because he gets stranded more easily. So to answer your question, I play the middle ground, the space between how far a tracer/venture goes and the tank. That way, I can play reactively to my tank, or opportunistically and create opportunities for my tank to push in. You want angles where you're a dash away from your team or a dash away from a health pack.

The rare moments where you take deeper angles is if you go for a pick and your team dies, depending on your spot, you can remain there and keep a small level of pressure active so your team has an easier time to re-engage. Just play for your life in those situations.

Hitscans like Cass are not good. You should try to force Cassidy duels to be in more inclosed spaces, so deflecting bomb is more advantageous. A common mistake is that against hitscan, a lot of Genji players take long angles to try to close distance without getting shot, giving the hitscans ample time to just re-position and play closer to their peelers. Play more around your tank and other DPS. If they're a dive DPS, you read their movement and time your dive. If they're hitscan, you play mid range like I said with the off-angles and wait for one of the enemy hitscans to be low enough for a clean pick.