1. Sales confidence - While not a metric measured in SFDC, you can work with enablement to craft a pre and post sales confidence metric to assess how confident reps feel in navigating competitive conversations.
2. Competitive win rate - You're likely already measuring win rate, but competitive win rate will give you a direct KPI to measure the improvment in closing competitive deals.
3. [ Product specific] Reduction in lost deals due to product capabilities - To measure this metric you'll need to be tracking lost reason and have a drop-down for reps to choose "product gap."
Positioning (which by definition is competitive positioning since it carves out a place in the market where you are the clear winner) is your strategy. It defines who you're for and how you'll win. As a result, not only pricing and packaging but your marketing strategy, product roadmap, partnership strategy, etc are designed to deliver on that position.