People keep comparing 2005 to 2021.
I was confident by May 2005 the Sox had a serious shot at the World Series. I do not have the same confidence this season. Here are the primary differences as I (and I believe many others) see them between the two teams:
Health: The 2005 lineup and starting staff was healthy all year. AJ played 128 games, the least among the nine starters. Half of the 2021 Sox lineup will be fortunate to reach 128 games this season, with starters Grandal and Engel likely having lingering issues and availability concerns through the playoffs.
Tested vs. Untested: The 2005 was a solid experienced team. A 30 year old second baseman was their "rookie". The 2021 team has three untested key rookie starters, one learning multiple positions on the fly and two with under 100 games over 2 seasons due to various injuries.
Manager: Ozzie managed the starting staff well, and more often than not pushed the right buttons when managing the bullpen, comfortable changing closers on the fly. Ozzie was familiar with the team, he and Kenny made moves in the offseason to address holes, they were ready to play. Tony does not have a handle on when his pitchers are gassed, prefers a push button approach and also did not have two key contributors capped in terms of usage.
COVID: Beyond Tony, the current team is coming off of the 102 game owner lockout from last season, and unlike 2005, we just don't know how the starters, especially Rodon and Cease, will hold up with the substantial increase in year over year innings.
Competition/ Home Field: In 2005, I didn't see any team the Sox' equal heading into the playoffs. In 2021, series vs. Tampa, Houston and New York seem to most as coin flips the Sox can win, but are not necessarily favored to win. There also appears to be a good chance the Sox will be going through all three rounds on the road, whereas the Sox had home field advantage throughout 2005. The NL has the Dodgers and other teams who are playing much stronger than the 2005 Astros if the Sox reach the World Series.
Can the Sox overcome these burdens / difficulties? Yes.
Are they facing a greater challenge than the 2005 team heading into the playoffs? Yes.
Do many people feel the consistent mistakes, poor close game management (Tony is 12-20 in one run games, Ozzie was 35-19 in 2005), Tony's obsession over platooning (hitting and pitching), sloppy baseball fundamentals under Tony La Russa (Tony's sloppy team is 25th in errors, Ozzie's team was 9th) , and poor bullpen management (Tony's team is 21st in blown saves (9 from bottom), Ozzie's team was tied for 11th despite having 3 closers) are likely to cost the Sox in October? Yes.
The Sox not only have to overcome solid playoff opponents but also their substandard manager, and substantial injuries. Despite going "all in" except for the manager position (AJ Hinch is having a great season in Detroit), there are many legitimate question marks heading into the postseason. This is the reason many fans have expressed legitimate concerns this year, regarding the substantial obstacles this team is facing vs. the 2005 team.