Unifi Dream Machine kit doesn't seem well suited to routing. Great for other shiny functionality but below par compared with a Mikrotik with a base of the same A57 quad-core ARM CPU.
Mikrotik's CCR2004-1G-12S+2XS uses an Amazon Annapurna Labs Alpine v2 CPU with 4x 64-bit ARMv8-A Cortex-A57 cores running at 1.7 GHz.
The UDM SE uses 'Quad-Core ARM® Cortex®-A57 at 1.7 GHz'. A big more digging and it's the same Annapurna AL32400 found in the Mikrotik.
The Mikrotik can push over 3.5 Gbit/s in each direction over each core simultaneously. I've done so with one, running 4 iPerf threads and getting 15 Gbit/s throughput, 3.75 Gbit/s/core. Each thread ran on a single core.
No idea why the UDM SE runs so far short but from the tests I've seen it's way slower single thread and multiple thread. The UDM Pro was abysmal as a router in my experience too. Mine is sitting it my loft where it's been living for a year in shame. My great thanks to Ubiquiti for making me move to Mikrotik: I've not regretted it.
Maybe they're just trying to do too much, with too much SW cruft running all the time. Just idling there is an avg of 25% of each core gone, and I think things like the traffic identification add some overhead as they all run suricata I believe. But even disabled I seem to struggle to get much through it. I don't think the PPPoE overhead helps, I've not tried a DHCP only setup.
It's a shame really as the hardware makes some nice choices; UDM Pro SE is quiet (if you don't put a disk in it), outwardly has a good spec CPU, good connectivity with 2x 10G SFP into the AL32400, 8 port POE gig switch and a single 2.5G copper port (albeit the latter is on a Realtek PCIe device). It's really for a me a bit of a sweet spot device for a nice home setup, and the management UI is nice.
I wonder how the Mikrotik devices fair with PPPoE added in the mix for a WAN interface? Maybe they're better at allowing you to allocate things to particular cores perhaps.
I'm not sure whether any of these ARM devices are really powerful enough if you end up doing much in SW (as opposed to offloaded). As a noddy test I just ran iperf3 as a server on the Dream Machine, and connected to it over the localhost interface from itself. The max throughput was 12Gb/sec. Have you tried that out of interest on your Mikrotik?
By comparison, a not particularly flash laptop (Lenovo E14 AMD Ryzen 4500U) is doing around 45Gb/sec on the same test in Ubuntu. Passmark for that CPU is 11000 all/2400 single core. A decrepit Mac Mini 2014 1.4GHz i5 (2400all/1400 single) is able to do 18Gbps in OSX. None of these machines are useful to me though for routing duties owing to lack of ports.
For now I've just bought a Lenovo M720q to experiment with; it's got a pretty good CPU benchmark at 7500 all / 1900 single (much better than the Celerons in most of the Chinese Amazon router computer boxes that seem so common now), it's tiny and a nicely built unit, and has a PCIE slot that will take an quad intel GBE LAN card that I've picked up. It will be an interesting datapoint to see how that behaves in some testing. I don't need to route more than 1Gbps, but I do need it happening I think in a timely fashion to facilitate fast single thread speeds.
