1. Cavaliers may have 3 Mov, but they still play pretty defensively due to the spacing requirements of Hone+Fortify Cavalry. Your use of Vantage in this case is offensive, putting other members at risk in the 4v4. Sure, you could let the enemy initiate twice instead, but that means you spent two turns when you could've spent one and gave up more space than necessary in the process.
2. Xander might be strong, but outside of Nino and Julia, he's not one-shotting the world any time soon. Not without Triangle Adept, at least.
3. With healers becoming actually viable, Quick Riposte can have a much longer, potentially infinite uptime.