The cost of the commute from TC vs. DB is rougly the same ...
DB to Central ferry (25 mins) will cost you $ 23.20 plus $4.6 for MTR from Central to CWB. The MTR from TC is slightly less but not much. The walk from the ferry pier to Central MTR is 10 minutes and the MTR to CWB takes another 10 minutes.
Btw, you can also take a bus from DB to Sunny Bay MTR ($8, 15 minutes) and hop onto the Tung Chung line MTR and go to CWB. It might take a little longer though but if you need to go to places on the Kowloon side this option is generally quicker.
There are two ways to get to CWB by MTR; either Tung Chung line to HK station, 10 minute walk to Central station, island line to CWB. Or change in Lai King to Tseung Wan line, take the MTR to Admirality and change for the island line there. You safe the 10 min walk between HK and Central station but the MTR ride will take an extra 10 mins so overall it's a wash (and same price). However, the Tseung Wan line is usually a lot more packed than the Tung Chung line.
I would note that the 'experience' of living in Tung Chung is vastly different from DB. TC is a 'new town' with large scale high-rise developments whereas DB is considered a 'resort community' with lower density housing (there are some high-rises but it feels less of a concrete jungle). DB also has a larger share of foreigners than TC and English is more widely spoken.
Like TC, Park Island tends to be more Chinese. For example, the menus displayed at most restaurants there are in Chinese only.