In order to click into a comment to edit its text, a single-click somewhere in the existing text does nothing. I have to double-click on existing text, which will select the word under the cursor. Only then can I single-click to position the cursor so that I can start editing.
That’s how it works on the Mac: a single click selects the comment, so you can do a right click to apply features like “Convert to Default Formatting” or “Convert to Footnotes”, and can select more than one or all using Cmd-A/Ctrl-A; hence you need a second click to enter the comment/footnote for editing.
You are correct, once a comment has been selected in the inspector a single click should be enough to begin editing. This has been filed.