Your whole post shows you do not understand.
You only have the ability to make a tackle or an interception when the opponent has the ball. You can't make a tackle or an interception when your own team has the ball, can you?!
If the opponent only has the ball for eg 30minutes in a match, that means you only have a 30 minute window where you are acting to make a tackle or interception. If you make 2 in that time you are doing 1 every 15 minutes.
If the opponent has the ball for eg 60 minutes in a match, if you make 2 in that time you have only managed to make 1 every 30 minutes.
The first case is being more effective as a ball-winner than the latter.
As per above, it is clearly more accurate, because you can't make a tackle when your own team has the ball. Just adding up total numbers assumes you can make a tackle when the opponent has the ball. Just looking at the total, not adjusted, distortedly swings tackles+interceptions stats in favour of players of the worst teams who tend to just park the bus, because their opponents have much more of the ball and they spend more time actually needing to defend.
Obviously it's not a completely perfect measure, but as far as defensive performance goes it's still a very good one. But also, winning the ball back for your team is still better than forcing your opponent to pass, as in the latter case the opponent still has possession.