Offline SMPS with discrete FET or controller/FET combination

I need to do a 15W, offline (230VAC) SMPS for V(out) = 24V
The SMPS will be completely enclosed in an enclosure with no ventilation.


We have a choice between using a PWM controller IC and a discrete DPAK FET, or an IC in a DIP package which contains the FET and controller on the same chip.



Please can you convince me that i would be better off using a TOPSwitch-jx in the eDIP-12 package ........
http://www.powerint.com/sites/default/files/product-docs/topjx_family_datasheet.pdf


......rather than an SMPS with a discrete DPAK MOSFET (STD4NK80Z)? http://www.st.com/stonline/products/literature/ds/9250/std4nk80z-1.pdf

-It's just that the DPAK package has a large metal tab on it, which gets soldered to the PCB, and provides excellent removal of heat from the FET package...

...whereas the eDIP-12 package has very thin legs through which the heat must be conducted to the PCB copper.

Therefore, it's obvious that the DPAK package will have far superior thermal performance than the TOPswitch-jx eDIP-12 package. -And since heat is THE worst enemy of any electronic component, why should i use a TOPSwitch-jx in the eDIP-12 package?

I appreciate that the eDIP-12 has a metal back to which a heatsink can be attached, -but we do not want to use a heatsink as it makes the power supply more expensive and less robust, since the heatsink requires conscientious attention by the assembly staff so that they.......
-use the right heatsink paste,
-use heatsink paste that's in date,
-apply correct quantity of heatsink paste, -
-apply the correct torque to the heatsink, etc etc.

So in summary, why should i use a TOPSwitch-jx, when using a PWM controller IC with separate, discrete FET will give far superior thermal performance?

Are these the only options? I suspect there will also be surface mount choices that are similar to the DPAK -- where the PCB can be used as a heatsink.