hehe, Drogba not top class, sure.
04/05 he only started 18 league games and got 10 goals and 5 assists. UCl 5 goals in 8 games.
05/06 he only started 20 games, got 12 goals and 11 assists, UCL 5 starts 1 goal
06/07 he started 32 games, 20 goals 4 assists, 12 ucl games 6 goals 1 assist.
07/08 17 starts 10 goals 6 assists, ucl 13 starts 8 goals 2 assists.
08/09 15 starts 5 goals 4 assists. UCL 7 starts 5 goals 1 assist
09/10 31 starts 29 goals 10 assists, ucl 5 starts 3 goals.
and on and on. In fact 10/11 is the only season in which he started a huge number of league games and didn't score a huge number of goals, he still got 11 goals and 13 assists in 30 starts. 05/06 was the only bad season he had in the UCL.
In general as others above, his game wasn't about just being a number 9, he had multiple fantastic years for assisting, his strike rate in the UCL was pretty consistently high. He pretty much got a goal or an assist in every season in 2/3rds of his games, in some seasons much higher, others a tiny bit less. However he also had a massive knack for scoring in the toughest games and he was around through Mourinho playing to use him as a often very isolated striker who spent huge portions of games holding up the ball and fighting defenders while waiting for support.
He was an absolutely top class striker because his scoring record was fantastic DESPITE being in a team which often favoured defensive play and having him work on his own so much. It's also rare for a player who is so dominant in the air, who can bully defenders and wear them down score so much. Him and Zlatan are almost alone in that regard. His record only maybe appears less good if you believe he started 34+ games every season like a lot of other top players have. 10 goals/5 assists wouldn't be much for 38 starts, but for 20 it's amazing.
This is also why Rooney is average, he also only has 2 seasons above 20 goals, and he has a similar scoring record to Drogba, but by and large he started many more games. From 04/05 starts Rooney had in the league is 24, 34, 33, i'll come back to 07/08, 25, 32, 25, 32, and on. 07/08 for some reason ESPN lists as 25 league games and 22 UCL games.... so I'm not going to take that one as certain
they have some random years thrown in where the data is wrong but the rest is normally accurate. Drogba only had over 20 starts in the league twice, both times he scored over 20 goals. Rooney had over 20 starts in effectively every single season and yet still only managed over 20 goals twice.