Sure Bremer is 4 years younger but he hasn't proven he's a top CB for several seasons, he's been at Torino (a mid-table Serie A at best) for 4 seasons now. I've seen so many CBs have one stellar season and then crumble. Signing him for the huge fee Torino are asking for is a gamble.
Rudiger, on the other hand, is proven everywhere. EPL, Serie A, Champions League and internationally. If we offer him a 4-year contract worth ~10m/season, he'll be 33 by the end of the contract and we can decide then if we want to renew with lower wages or release. IMO, it's reasonable as long as his agent doesn't require a crazy sum for his commission.
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I don't know. MDL seems happy in Turin and with Allegri. If we agree a contract extension as reported recently, he's staying at least for two more seasons.