There have been far worse queens, I assure you. If it wasn't for the baby and the crystalized husband she would be totally focused on her job.
We've seen how much better and well-developed Monster Town is compared to Mewni, they even have a stadium.
Also, mewmans problems are not known by Eclipsa because they haven't told her... which anoyed Moon a lot.
She also practiced pidgeon language for her dinner with the pidgeons and was able to save the Spiderbites situation. Not to forget she was ready to sacrifized Heinous in Season 3 and her husband's freedom for the sake of the kingdom in Swim Suit.
She is not that bad but needs more support and less distractions. Someone please find a competent babysitter.