C'mon: What is micro USB rated for? 1.8A maximum. Have you ever had a look at the tiny contacts?
Did you measure whether voltage drops occur or not? That's the question! With micro USB they occured and using the very same PSU (with USB type A to 5.1/2mm barrel cable) and the soldered barrel plug they don't. Problem solved!
Do you know why everyone in the industry who's not mad in the brain doesn't use this shitty connector? Do you realise that responsible vendors don't use this crap even for charging?
Do you know when voltage drops will occur when you use a crappy DC-IN? Only when consumtion is high!
Did you already measure (of course not!) what happens when you cool the A83T with a fan and let it operate under high load? Consumption of the CPU cores alone will easily exceed 8W (and your connector is rated 1.8A/9W max. so there's "not that much room" for the additional 5-6W connected USB peripherals, a SATA disk and the display engine driving a connected display will need).
Choosing micro USB for a power hungry SBC is braindead. And the current available from the PSU is nearly irrelevant because you run into undervoltage/undercurrent situations way before the current limit is reached. Again: micro USB is rated for 1.8A max and might be able to provide 2A under best conditions (heating up the tiny little contacts!)
The PSU I use is rated 5V/2.1 and I used it over the years to power/measure all sorts of things. When you combine it with a cable with barrel plug it's always fine. When you combine it with micro USB it simply sucks when consumption increases:
This is what happened with a boring old Banana Pi M1 (not able to consume more than 600mA/3W under full load when overclocked). The very same PSU and cable used with the M3 and its A83T isn't sufficient enough. And this is just general knowledge, no need to discuss.