The Order of Wizards (Q. Heren Istarion) was the title assigned to five Maiar in the Third Age of Middle-earth. The wizards were commonly known as the Istari (Quenya...
tolkiengateway.net
The Istari is the title of the second section within Part Four of Unfinished Tales of Númenor and Middle-earth. In the section is described the background of the...
tolkiengateway.net
The Order of Wizards (Quenya: Heren Istarion), or simply Wizards (Q.: Istari), were a group of Maiar sent to Middle-earth by the Valar in the early Third Age[1] around TA 1050 when the "Necromancer" became active in Dol Guldur.[2] They were embodied as elderly Men and entrusted to aid the Free...
lotr.fandom.com
I can go on. There are no "wizards" who aren't Istari and no Istari who aren't "wizards". But their power comes from being Maiar, and there's no dispute on that.
You're perhaps confusing Istari and Maiar? There are Maiar who aren't Istari, who are generally range about equally powerful to significantly more powerful.