Panel a: black hole accretion rate as a function of the SFR for J1015+0020 (magenta star) compared to the sample of z ≳ 4.5 QSOs described in Sect. 4 and five WISSH QSOs from Bischetti et al. (2017), Vietri et al. (2018), Duras et al. (2017). Orange (red) stars refer to the [CII](continuum) emitters detected in the ALMA map. The locus of points with unitary mass loading factor is also indicated by the dashed line. Panel b: present BH vs. host galaxy growth timescales, derived assuming constant Ṁ_acc and SFR equal to the observed values. The dotted, dashed, and solid lines indicate a 10:1, 1:1, and 0.1:1 growth timescale, respectively. Panel c: exponential BH vs. host galaxy growth timescales, derived assuming constant λ_Edd and SFR/M_dyn. Lines as in panel b.