Belichick ... does many things very well but he has achieved nothing in head coaching career without Tom Brady, and frankly there is nothing to suggest he would,
Usually this line is only trotted out by fans of other teams that are seeking a way to discredit the success of the Patriots; I'm surprised that you would play that card.
Belichick inherited a very bad Cleveland team that was old and bloated with contracts that needed to be dumped. Despite the bare cupboard, the Browns doubled their number of wins in his first season as head coach. The following year they were doomed with injuries, having to start three quarterbacks - including the immortal Todd Philcox - yet still managed to increase their win total.
In Belichick's third season he finally had enough of Bernie Kosar, and replaced him with Vinny Testaverde. However, Testaverde was injured and he had to revert to Kosar. Cleveland's record remained the same as it was the previous season, 7-9, one win below .500.
The next year the Browns improved again, winning four more games than the previous season. They made the postseason, and won their first playoff game in five years. As it turned out, they have not won a playoff game in the twenty years since that victory over Bill Parcell's Patriots.
The next season the Browns started out 3-1, with their only loss in week one at Foxboro by three points. At the time they looked like they were one of the best teams in football. Then Art Modell announced he was moving the team, and chaos ensued. End result was a 5-11 season, and Belichick was fired.
His two other seasons without Brady were his first with the Patriots, in what was obviously a rebuilding year, and the 11-win 2008 season.
Belichick admitted that he should have handled the Kosar situation better. He learned from it. As far as the final season in Cleveland, there was no precedence in sports to draw knowledge from. Again, it was another valuable learning experience - but I don't know if there are/were many (if any) coaches that could have held the team together in that circumstance; let's not forget it was exacerbated by a meddling owner that didn't have his back. He left a very good team behind, and one that was well set for the future. For example, one trade that he had made for the following year was a draft pick that turned out to be Ray Lewis.
To me the notion that "there is nothing to suggest" that Belichick would ever achieve anything without Brady is extremely shallow, superficial and off-base.
It might be time to read Halberstam's
The Education of a Coach, and view NFL Films'
Cleveland '95.