The claim that Ibn Taymiyah went against 4 Imams and he had no Salaf in his fatawa.
In response Shaykh Safi al-din al Hanafi the Matureedi (d 1200 h) said in his book
القول الجلي في ترجمة الشيخ تقي الدين ابن تيمية الحنبلي that:
“قد نص على أنه بلغ رتبة الاجتهاد جمع من العلماء؛ منهم الإمام أبو عبد الله الذهبي، والحافظ ابن حجر، والحافظ السيوطي في طبقات الحفاظ، ولم يتفرد بمسألة منكرة قط، وإن كان قد خالف الأئمة الأربعة في مسائل فقد وافق فيها بعض الصحابة أو التابعين”
This is clear that He (Ibn Taymiyah) reached the level of Ijtihaad, A group of scholars mentioned this. Among them are Abu Abdullah ad-Dahabee, Hafidh Ibn Hajar (al asqalani) and Hafidh as-Suyuti in Tabqaat al Huffaadh. He was not alone in any of his fatwa, even though he disagreed with four Imams in Masaail but those were in agreement of some companions or Tabiyeen. [al Qawl al Jalli fe Tarjuma Shaykh Taqi al Din Ibn Taymiyah al Hanbali page 6, Ghayat al Amani 1/484]
Safi al din al Hanafi said in the introduction of his book.
فهذا جزء لطيف في ترجمة شيخ الإسلام وبركة الأنام علم. الزهاد وأوحد العباد سيد الحفاظ و فارس المعاني والألفاظ تقي الدين أبی. العباس أحمد بن عبد الحليم بن مجد
This is a small tract giving a biographical sketch of the Shaykh al Islam Ibn Taymiyah, who is blessing for the people, a sign of the pious, a great unitarian from among HIS servants, a leader of the conners, a cavalier of words and ideas, known as Taqi al Din abul Abbas… [al Qawl al Jalli page 1]
Shaykh Safi al Din was a Mautureedi Imam of his time and went against few stances of Ibn Taymiyah like Travelling to visit the graves and the issue of divorce but he defended his aqeeda and refuted the claims of the likes of Taqi al Hisni (the liar who said Ibn Rajab Hanbali made takfeer of Ibn Taymiyah) and Ibn Hajar al Haytami that Ibn Taymiyah was a Mujassami. Apart from Aqaid, he also defended his stance on fiqhi issues like divorce etc that Ibn Taymiyah was not alone giving these fatawa.
Before him various scholars said this for example Ibn Kathir said: