Please, know that the only way a low-leveled account can be in a party with a higher level account is through cheats.

IMO :
If max level (271) character and level 1-194 or level 1 character and level 51-max level character are in a party by a single invite (max level inviting level 1 and the party suddenly created in a single click without bridging the low-level or vice-versa), I assume that's obviously a cheat.

But, if they literally bridging the party with legal requirements and flagged as a cheats... Then you must be kidding me!!! Its the game feature that exist since long-long-time ago. The main purpose was for helping newbies. You might invite any low level by bridging the low-level into your party (and vice-versa) with some legal requirements.

Last but not least, I don't have any intention to say this.. but, banning any accounts which bridging the party in legal ways isn't a win-win solution for innocent players.
Thank you.