Front-end and back-end almost always use different build/debugging tooling, different unit/integration testing frameworks, and even different paradigms. Unless your developers are good at constantly switching modes, it's hard.
"no real upside" is wrong, as you point out, but I would stand by "no guaranteed upside" :-)
In practice, Point 1 isn't too realistic though:
Front-end and back-end almost always use different build/debugging tooling, different unit/integration testing frameworks, and even different paradigms. Unless your developers are good at constantly switching modes, it's hard.
"no real upside" is wrong, as you point out, but I would stand by "no guaranteed upside" :-)