I will present ALMA Compact Array (ACA) 870 micron data of 28 infrared-bright SDSS quasars at redshifts 2 – 4 with estimated star formation rates beyond 1000 solar masses per year, the largest such sample ever observed with ALMA. The majority of the sources have unique ACA counterparts down to 3" - 4"resolution within the SPIRE 250 micron beam, centred on the SDSS coordinates. With only a handful of clear cases of multiple sources within the SPIRE beam, these results are in tension with works on the multiplicity of SPIRE 250 micron sources and sub-millimetre galaxies. I will present an extensive comparison between these findings and other recent works and will discuss the implications in the scenario supporting major mergers as triggers of the brightest AGN.