However, particulate filters aren't necessarily required to bring gasoline engines into compliance. Turbocharged DI engines can be particularly bad, especially in boost enrichment, but there's plenty of examples of engines that are fine.
Let's use the 2015 2.0 DSG TDIs (they're all certified together, using a Jetta as the representative model) as our baseline.
2015 Volkswagen Jetta TDI, DSG: .0020 g/mi on "CVS 75 and later (w/o can. load)" test cycle
For comparison, there's four production gasoline engines at or above 40% thermal efficiency - the Toyota ESTEC 2ZR-FXE as used in the 2016+ Prius and Prius Prime, the Hyundai Kappa III 1.6 GDI Atkinson as used in the Ioniq and Kia Niro, the Toyota A25A-FKS as used in the 2018+ Camry, and the Toyota A25A-FXS as used in the 2018+ Camry Hybrid. There's no PM results for the Ioniq or Niro, so they'll be left out.
So...
2018 Toyota Prius, Li-ion battery: .0003 g/mi on "California fuel 3-day exhaust" test cycle, .0013 g/mi on US06 test cycle
2018 Toyota Prius, NiMH battery: .0002 g/mi on "California fuel 3-day exhaust" and US06 test cycles
2018 Toyota Camry Hybrid LE: .0001 g/mi on "Federal fuel 2-day exhaust (w/can load)" test cycle, .0002 g/mi on US06 test cycle
2018 Toyota Camry Hybrid XLE/SE: .0001 g/mi on "Federal fuel 2-day exhaust (w/can load)" test cycle, .0007 g/mi on US06 test cycle
2018 Toyota Camry XLE/XSE: .0001 g/mi on "Federal fuel 3-day exhaust" test cycle, .0015 g/mi on US06 test cycle
Note that all of these are unfiltered gasoline engines, and the Camrys are even direct injection, and they're beating the (filtered) TDI. The last one isn't even a hybrid. The solution is more displacement and Atkinsonization through variable valve timing, really.
Of course, this isn't considering PN, just PM, so microfines could be a problem especially on the Camrys.
Edit: Let's add ADAC EcoTest results, for the European market. The Camry isn't sold there, and the A25A hasn't appeared in anything destined for Europe yet (best bet will be the RAV4 I'd guess), but there are ADAC EcoTest results for the Ioniq.
Toyota Prius Executive: PM: 0.2 mg/km, PN: 2.22183 10¹¹/km
Hyundai Ioniq Hybrid Premium: PM: 0.0 mg/km, PN: 29.3351 10¹¹/km (read: holy crap the microfines)
Skoda Octavia Combi RS TDI DSG: PM: 1.5 mg/km, PN: 0.00473 10¹¹/km (this is the closest I could get to the US cars within VAG for the September 2016+ version of the EcoTest)
So, basically, the TDIs are able to control the microfines better, but the gassers have lower mass.