If anyone divides the singular G-d into 3 personages or 10, yes, I would call them heretical.
A true Kabbalist is not doing that. The 10 Sephirot are attributes not persons or divisions of G-d.
That is why amongst Judaism, study of Kabbalah is recommended only after the age of 40 and that assumes a person has studied Torah already since childhood.
Your fellow Karaite Jews sharply disagree with you. I have asked Karaites their opinion of the Kabbalah, they mince no words, calling it abominable, polytheistic, witchcraft.
I am over 40, by the way. I have read Gershom Sholem, etc. Anybody without a religion to defend, in your case Judaism, can see the sephiroths, mere attributes you call them, are but a form of occult theosophy.
It is widely known that occultists like Helena Blavasky adopt Kabbalistic principles and use them in their evil systems. So do the Freemasons and witchcraft systems. Just about everything on the evil, satanic, occult side uses the Kabbalah. The Karaites are right.