What problem does this address?

Often times the user knows already which level of heading they want to use.
The slash command is a great shortcut to insert the heading block. However, it always starts at the level of h2 as a default. If the user wants to add a heading block with another level, they must type in /heading and then manually change the level by selecting one in the toolbar.

What is your proposed solution?

It should be possible to type in /h1, /h2, /h3 as a slash command to add a Heading block with the correct heading level.