[C II]-to-FIR luminosity ratio as a function of FIR luminosity. Observations of star-forming galaxies and LIRGs at z < 1 are shown with light blue crosses. We report the star-forming galaxies at 1 < z < 5 with orange arrows. RQ quasars from the literature are depicted with grey points. All references for these data are reported in Sects. 4.1 and 4.4. The circles indicate the RL quasars observations from Khusanova et al. (2022), Venemans et al. (2020), and Banados et al. (2024b). The squares indicate the values derived in this work, assuming that the total measured ALMA continuum flux is due only to dust, all color-coded for radio loudness parameter. We note that RL quasars occupy a similar parameter space of that of RQ quasar hosts, with the exception of the sources J0131-0321 and J0410-0139 (with L_[C II]/L_FIR ∼ 10^{−3.5 − 4}). When considering FIR luminosities accounting for the synchrotron contribution-derived flux (red squares for sources from this work, red circle from Banados et al. 2024b), even the above mentioned outliers move closer to the locations of the RQ quasar hosts.