Very good point. I think the problem of slip fielding and batting in consistency lies at the same place. It's not about fielding capabiltiy. It's about concentration. To be a good batsman, to need to keep concentrating on everyball. And same thing goes for slip fielding also. That's why you would see most good batsmen make fine slip fielders.
So we need to improve our concentration capability to be good slip fielders or good batsmen.
And Allah Knows the best