the highest version number of an extension shall be shown
What do you suggest?
If you search for an extension, then the extension key is listed with the most recently uploaded version. The highest version should be used instead.
A user normally needs the extension in its highest version number and not in an older version. Most users won't see that a higher version of this extension is also available.
Add an use case
Search for tt_products. You get version 2.7.30 which does not work under TYPO3 8 instead of version 2.8.19 which works fine under TYPO3 8.