[talky]

There are many insecure bosses who will surround themselves with deputies who are less capable so that they do not outshine the bosses or be a threat to their position.

this is universally true fr history to today to in  the future.
chao chao of 3 kingdom was careful of xi ma ya n he was right after all 
after his death  this xi ma ya overthrown his sons kingdom

[twinkle07]

but tharman ish capable

[Ola]

In Singapore's history, the role of the DPM has always been filled up by loyal but uninspiring and/or non-threatening bureaucrats.

Teo Chee Hean, Wong Kang Sing, Tony Tan, Goh Chock Tong, Heng Swee Keat etc. The few more able ones like Jaya Kumar and Tharman are either no threat because of their skin color or promptly put down by LKY like Ong Teng Cheong.

Anyway the DPM role is largely symbolic, there is no indication so far that a DPM has any real control or influence outside of his own ministry. In fact I reckon a Coordinating Minister probably looks after more ministries and government organs compared to a DPM.

Heng, arh!

No Cotton nor Shoot Blank Queen as DPM

or else SG will have riots.