I think a lot of the surface finish at this fine extrusion level is dictated by vibration. Bearings, rolling wheels, belts, motors, resonant vibrations. The filament being layed down is so thin that it seems to cool very quickly and all the little pressure vibrations in the filament get locked in place before they have a chance to relax and dissipate.
Yes I think you're right, be we must take in consideration that a glossy black is the worst case scenario, but I like this filament it's ESUN PLA+ very sturdy can make a .25mm circular plastic band and it will not break under stress unlike native PLA and it's relatively cheap 30$US per Kg often is special at 20$
Furthermore, the extrusion speed is very slow. The gear on my titan aero barely moves when I'm printing at 0.05mm layer height. I think at that low speed some extrusion steps are getting missed.
I've bought a twin gear metal extruder to help reduce this
but must pay the price in weight event it's only 250gram ( no much higher than your Titan) . Bowden setups reduce all this but hysteresis on the retraction is a pain for small details
This has been discussed before in another thread. Increasing the microstepping value for the extruder can help, but you can then run into hiccups and missed steps that way. @wilriker even made a calculator. https://wilriker.github.io/microstep-calculator/
I really like the look and feel of 0.05mm layer heights. It feels almost like an injection molded part, but there are so many new artifacts that get exposed when the layer lines go away. I've given up on such low layer heights entirely until I have a printer more capable of the resolution.
Something like the RailCoreII which has shown incredibly detailed prints at very low layer heights.
0.15 layer height with a 0.6mm nozzle is my new favorite. You can print
Nice Turtle! I do mostly mechanical part and .6mm don't give the clearance I want.