Resize different text proportionally inside text box

Sometimes I have text with different sizes inside the same text box and it's quite common that I need to resize the text, proportionally, but using the Transform Tool is not ideal, because it resizes the text box itself, which is not always the goal.

Someone suggested a "solution" here (https://community.adobe.com/t5/photoshop-ecosystem-discussions/change-text-size-without-transform-tool/m-p/12823671#M630782), but there's an issue with using a shortcut to add X amount of points. All text will be added X amount of point, but that is not how percentage works, so it will not keep the relationship betwen the different text sizes. Example:

Title at 50pts

Sub title at 25pts

Title is double the size of Sub title

Adding 50pts to each:

Title is now at 100pts

Sub title is now at 75pts, which is not half of Title.