Yes, it is less efficient. However the numbers are rather small:
Most modern laptop processors, including the ones on the Framework, have a TDP of 5-45 watts. Framework chargers are rated for 60 watts.
Your response also assumes a more efficient alternative is available. I work as a professor at a community college. I fix old laptops and give them to students who have no means to afford a computer. For many, that upcycled gift has gotten them through their bachelors degree.