I own this machine and have since moved on from it for the exact reasons you stated.
It is possible to create microfoam that is good enough for making clearly defined latte art on the Delonghi Dedica but it requires practice (as would doing the same on any machine). You did the right thing by removing the metal sleeve but the main problem is that the steam power is relatively weak and so it makes it harder to create the vortex required to properly incorporate the aerated milk. Focus on trying to create a spinning vortex/whirlpool type effect in your milk as this is the most important step in ensuring you end up with silky milk.
- Aerate the milk by keeping the tip of the steam wand near the surface of the milk. You should hear spitting noises. This will introduce air into the milk.
- Once you have aerated enough, dip the tip of the steam wand below the surface and try to form a vortex/whirlpool.
- Spin the milk as in step 2 until the milk is at the right temperature.
For good latte milk, you should not over-aerate. A good starting point is simply raising the height of the milk in your pitcher by about a centimetre. Once again, however, it will require practice and even then it may not be perfect due to the lack of steaming power this machine has.
The Delonghi Dedica also uses a pressurised portafilter basket which means that the crema you find in your cup is a result of artificial pressures produced inside the basket (similar to how Nespresso machines make their 'crema'). You can attempt to create darker crema by making the pressurised basket not the limiting factor of extraction by grinding finer (but not so fine as to choke the machine).
Temperature-wise, you want to ensure that your portafilter is heated by running empty shots through it as it will cool down the shot as it moves through the portafilter. The steam is also not as hot as commercial machines as they have dedicated boilers for the steaming rather than interchanging between functions within a few seconds like the Delonghi.
In conclusion, if you enjoy your coffee the way you make it, stick with the Delonghi Dedica but if you put a lot of value in the quality of the crema and being able to pour latte art then you might want to consider an upgrade or investing more time into practicing milk steaming.