Bronze 5 with a relatively high B5 MMR is better than bronze 5 with an average B5 MMR is better than B5 with a low B5 MMR
Pretty much everyone places lower than they were the previous season by around a full tier. I also wouldn't trust MMR estimates at this time of year, as they're only estimates and not your true mmr which only riot knows. This time of year in particular estimates tend to be wonky since some places use data from games actually played during preseason (pre-mmr reset, and hence inevitably wrong), and even the ones that are careful of that are estimates based on looking at the games you've played and the games of the other players in your games, and theres not a lot of data in that regard this early in the season.