I have several ideas to improve the toolbar. The image below is a small summary.
Being able to add shortcuts for sizes in the same way we already do for colors / colours.
The bar that separate colours and sizes from the rest of tools could be moved to the left so we also have a more efficient time when working with them.
To prevent other inconveniences with losing time when changing tools, it would be perfect to have the option of changing the order of the tools according to your preferences.
Lastly, other option for colours and sizes is allowing the user to customise o predifine several shortcuts with sizes and colours all in one click.