He (Al-Husayn bn Aliyy Al-Karaabeesee) was an innovator for various other reasons.
His book Kitaab al-Muddaliseen really exposes him. Al-Imaam Adh-Dhahabee himself said the book is filled with items that aid all other people of Bid'ah such as the Khawarij and the Shia against the People of Sunnah.
Also his 'lafdhee bil Qur'aan gayr makhlooq' was a smokescreen to attack the people of Sunnah, and to aid the position of the Jahmiyyah. This, Al-Imaam Ahmad knew about him, more than me and you, because we didn't live with both, to make him declare him a mubtadi. Many other scholars of the time followed suit.
Don't forget that he was referred to as a mutakallim.
His matter became worse when he began to speak ill of Al-Imaam Ahmad. At that time, nobody would speak ill Ahmad except an innovator.
He was an example of a big scholar that saqata (fell down from grace). The muta'aakhiroon can't save him from that suqoot.
He innovated Lafdhiyyah, and that is blameworthy. It is never a core of our Aqeedah to say lafdhee bil Qur'aan makhlooq, even though it is true. It is never a core of our Aqeedah because it can lead to evil. So it is wrong to say that is what we worship our Lord with. Rather what we worship our Lord with is Al-Qur'aan Kalaam Llaah ghayru makhlooq.
Al-Imaam Al-Bukhaaree, Al-Imaam Muslim, etc, also believe it is right but they would never make it a canonical statement.
So making it a canonical statement is bid'ah and whoever says it is a mubtadi, just as Karaabeesee who innovated it was.
This is a simple thing to grasp to save one from indulging in veiled Ilm kalaam.
This is the position of the scholars of Sunnah, past and present.
والعلم عند ربنا سبØانه وتعالى.
