Yes because I don't think Keane is that bad either. Keane had a couple of seasons with us where he was fine and got into the England team. We then played a style where Keane had to play in a higher line and got exposed. This is exactly what will happen to tarkowski.
Some defenders look good when they can defend deep and play it simple. Keane and tarkowski are two of those types. As you saw against forest we had the emphasis to push on and tarkowski struggled just like Keane does. They prefer playing In a deep back line.
For that reason I don't see him as an upgrade on Keane but a like for like