Both 'mins availability' and 'mins played' metrics are perhaps not precise to paint an exact picture of the injury situation. One could be preferred over the other basis the position of the player, utilisation of squad, formation, etc. For instance, with 'mins availability' metric, situations where a player although available in a game for 90 mins was fit to play only for an hour. Calculating availability in such a case and fairly assessing the situation is inconvenient.
In our case, from the defense perspective, even with the mins availability metric, percentage wouldn't skew much. If we consider Varane and Martinez to be our starting CB all the time then there were barely any games where either of these were available(fully fit) and were kept on the bench. They were mostly unfit/unavailable. In fact, several times, although available, they weren't fit to play the entire game. So, I reckon mins played for them won't alter much with the availability.
On the other side, the attack/midfield situation is different, and availability metric can give a substantial contrast with mins played since players have been rotated quite often throughout the season in these areas. Moreover, these sections observe relatively frequent substitution of players. Also, several players like Anthony, Rashford, Mctominay, etc. all at times available but have shared their mins played due to form, formation, tactics, etc. Thus, may create a wider rift in these metrics.
Nice work OP. Probably, if you could share mins availability too just for comparison.