Considering your tennis training statistics, which include a substantial amount of time (over 60% of the session) spent in Zone 3 (70-80% of max HR), this indicates that tennis is providing a significant cardiovascular workout. This intensity level is beneficial for building aerobic capacity and endurance. Your average and maximum heart rates suggest a workout of moderate to high intensity, comparable to what might be achieved in a medium-intensity cardiovascular workout.
Given this, it might be more beneficial to replace your cardiovascular routine with tennis, rather than your HIIT routine. Tennis in this case appears to mirror the steady heart rate elevation associated with traditional cardio exercises but might not reach the peak intensity (seen in Zones 4 and 5) typically targeted in HIIT workouts. This can help maintain your cardiovascular fitness while also incorporating the varied physical and mental engagement that tennis offers.
However, if your cardiovascular workouts are typically of lower intensity (more time in Zones 1 and 2), and you want to maintain or improve high-intensity performance, keeping the HIIT sessions and replacing them with tennis might not yield the same benefits in terms of peak performance and high-intensity stamina.