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tokens: from SIMBA are consistent at f gas 0.5, but significantly differ at f gas > 0.5 due to steeper decrease compared to our data. Such a sharp reduction in δ DGR translates to relatively low number of DSFGs with M dust / M ⋆ ≳ 0.01 produced in cosmological simulations. By investigating the connection between the δ DGR and Z gas in SIMBA, we find that very low δ DGR in galaxies from the highest-end of gas fraction is a result of their gas metallicities being lower by a factor of ∼4 relative to solar. The comprehensive treatment of different physical mechanisms that could be responsible for relative shortfall of model predictions, along with numerical limitations, is out of the scope of this paper. In the following we briefly emphasize their importance. The dust growth timescale is too long. One of the most critical parameters that describes the dust mass growth is the accretion timescale ( τ acc ). It is often modelled as: where a is a dust grain size which is usually assumed to be spherical with a typical size of ∼0.1 μ m ( Asano et al. 2013 ). The n H and T gas are the number density and temperature of the cold gas phase, and τ acc, 0 defines the timing of growth activation. The timescale for dust growth in the ISM changes as a function of gas surface density for different Z gas (see Popping et al. 2017 , their Fig. 1). If we apply M gas of our DSFGs, along with their compact ALMA continuum sizes (see the next section), we infer high median molecular gas surface density of ∼6.7 × 10 3 M ⊙ pc −2 . Such a high surface density implies short accretion timescales, on average τ acc ∼ 6 × 10 5 yr. These will be obtained if τ acc, 0 10 6 yr which is shorter than what has usually been adopted in cosmological simulations 6 . The short τ acc are proposed by Pantoni et al. (2019) , and are also reproduced in very recent semi-analytical models that claim fairly good overall match to the observations ( Triani et al. 2020 ). These are also in line with De Vis et al. (2017) , who found that variations in dust growth timescales might help to explain the M dust deficit at high gas-fractions in their large sample of nearby galaxies. Given the SIMBA’s ∼kpc resolution, a multiphase galaxy ISM cannot be resolved, which prevent us from knowing the exact dependence of the modelled dust content to the gas surface density. As a result, parameters such as the reference τ acc are tuned in order to boost the effective gas density. Thereby, it seems likely that use of shorter accretion timescales (equivalent to the increase in dust growth efficiency) in simulations could help partially overcome the shortfall to data. Dust destruction is too efficient. It is also possible that the dust destruction in simulations is too efficient. The total rate of dust mass destruction is given by Ṁ dest ∝ M dust / τ destr , where dust destruction timescale is usually approximated as ( Slavin et al. 2015 ): Here Σ M gas is the surface density of molecular gas mass, f ISM is the value