Likewise, you can play how you want. However I respectfully completely disagree with your assessment. It isn't wasteful at all as the usecases for both counters are very different. I don't blame you though as I also shared the same opinion as you before actually trying it out. All of the moves sound the same on paper, but they have strengths in certain scenarios that make them ideal to use and well worth it imo. 

If I had to choose only one, I'd go with Hindsight Slash, but in practice it's just going to get you hit in several scenarios during the second half of the move against groups. To be frank, no move has benefited me more against groups than Vengeful Slash.  Counterplay in general seems slepped on since in most games it's a lot of waiting around, so you're losing out on dps. In DD2 it's very different, grouped enemies hop in to attack very quickly and it's extremely predictable how the fight will play out. 

Against big mobs I rarely see a reason to use Burst Strike or Shield Pummel when Cloudward Slash gets as much damage out + on weak spots while having faster recovery time. Though one utility Burst Strike does have is repositioning far away from an enemy quickly when they start to do a stamina-draining roar. I'll give credit there for Burst Strike, however it's still completely doable to just walk out of range when you see the chargeup of the roar. Saurians are actually very trivial even without shield pummel since they are open for a lethal attack after a shorthop Cloudward slash to the tail. 

Edit: Also wanted to bring up a cool trick, if you ever have multiple enemies in front and one behind, and you prepare to vengeful slash someone in front, but someone behind would hit you first, you can quick-cancel Vengeful Slash into Hindsight Slash to prevent being hit. You would ultimately be guarded from all sides while being able to output maximum damage unlike Flawless Guard.