Please read the key points directly under the part you posted in ToS; they are specifically referring causing others death or damage. There is no mention of doing a fight solo or not. It’s specifically geared towards griefing.
I wholeheartedly think we should all be discussing a better way to do tanks/healers etc, but before throwing ToS out there please read it, internalize the words written and really take a minute to work out what they are saying.
Key Points:
It is prohibited to interfere with the combat of others in the following manner:
Using actions during combat to cause other players to fall from platforms or field areas to incapacitate them.
Using and manipulating enmity-related actions in an effort to incapacitate other players or interfere with gameplay.
Gathering groups of enemies to obstruct the view of others.
If a report has been filed and the prohibited activity is confirmed, a penalty will be issued.
Simply performing the acts listed above will not immediately result in a violation, as they could be caused unintentionally or be due to unintended circumstances. If it has been determined that the above behaviors were done intentionally or repeatedly to obstruct the other player's gameplay, then a penalty will be issued.
Please note that Square Enix may issue a penalty in its discretion even if a report has not been filed but the act was found being conducted in public areas such as in towns/cities/field areas, or online video/streaming services.