In your terms it's no more backward than only carrying the internal weapons on F-35 when you want the LO fit.
The F15SE has the exact same internal weapons capability as the F35B but on the JSF the sensors and kit are already part of the airframe, you don't have to take them off to maintain your day one 'stealth' such as it is and the capabilities that those bits of kit give you. Whereas with the SE's strike capability for day one 'stealth' you have to take all that useful 'stuff' off to maintain 'stealth'.