The short answer is no.
It is certainly not the case that everything found in classical books of history is sound, rather it is made very clear by scholars, including scholars of history, that this is not the case.
Such a broad statement cannot even be made with regards to Hadith books, which have far more rigour in authenticating narrations than books of history. The only book will say is absolutely authentic is the Holy Quran, although Sahih al-Bukhari and Sahih Muslim come close, because all of the Musnad narrations in them are authentic.
فما يكن في كتابي هذا من خبر ذكرناه عن بعض الماضين مما يستنكره قارئه، أو يستشنعه سامعه، من أجل أنه لم يعرف له وجها في الصحة، ولا معنى في الحقيقة، فليعلم انه لم يؤت في ذلك من قبلنا، وإنما أتى من قبل بعض ناقليه إلينا، وإنا إنما أدينا ذلك على نحو ما أدي إلينا (تاريخ الطبري)
Regarding what is in this book of mine of narrations that I have mentioned from people the past, that causes the reader to feel it is baseless, or its hearer to disapprove of it, because he does not know it to be sound, or feels it does not reflect reality, let it be known that it was not invented by me. Rather it was narrated to me by narrators, and I have narrated it in the same that it was narrated to me (meaning with its chain of narrators). (Imam Abu Ja’far al-Tabari, Tareekh al-Tabari).
The statement of Imam Tabari above summarises for us the general approach taken by scholars of Tareekh, especially early scholars. They would narrate information with the chain of narration (Sanad) and leave it to scholars who came after them to investigate the authenticity of the chains. Therefore, it is not surprising to find weak and even fabricated narrations in books of history.
– Answered by Shaykh Noor ud-deen (04.01.2021)
Seerah books are not completely authentic
How many wives did Sayidina Hasan have?