Khalid ibn Walid slaughtered the Banu Judhaimah, when this news reached the Prophet (ﷺ) he said: "O Allah! I am free from what Khalid has done." (Sahih al-Bukhari 4339). Also he killed Malik ibn Nuwayrah and slept with his wife, 'Umar wanted to stone him for adultery and punish him for killing a Muslim and called him an enemy of Allah. (Tarikh Al-Islam 3/36, Jami Al ahadith 13/94, Tarikh at Tabari 2/274)
According to the Ahl al-Sunnah, Khalid bin Waleed was a good Muslim, further he was a Sahabi and the sword of Allah - which is the title that the Prophet ﷺ gave to him.
نعم عبد الله وأخو العشيرة خالد بن الوليد وسيف من سيوف الله سله الله عز وجل على الكفار والمنافقين
What a good slave of Allah and a brother of the tribe Khalid bin al-Waleed is, he is a sword from the swords of Allah that He has unsheathed against disbelievers and hypocrites.
لا تؤذوا خالدا، فإنه سيف من سيوف الله صبه الله على الكفار
Do not offend Khalid, for he is a sword from the swords of Allah which Allah has drawn on the disbelievers
As for Bani Jadhima, the Prophet ﷺ sent Khalid with an army to fight them. However they accepted Islam, but they did not express their acceptance in a clear way rather they said Saba'na whose meaning is ambiguous. So Khalid did not spare them. This was a mistake of ijtihad and Khalid did not willfully transgress the law. A person is not accountable for making such a mistake in his judgement. We know that the Prophet ﷺ did not enforce any legal punishment (execution for murder) on Khalid because it was a mistake.
As for Maalik ibn Nuwayrah, he was an apostate: He refused Zakat and he referred to the Prophet ﷺ by calling him صاحبكم ('your' companion) which displayed his own disbelief. Khalid was either correct in killing him. Or he should have established more clear evidence or waited for a command from the caliph - in which case it is again a mistake of ijtihad. And as for sleeping with his wife, Khalid either married her or made her a concubine, there was nothing wrong with that. Any reports on this marriage are weak, such as what you have cited about Umar's statement. Again Abu Bakr did not impose the legal punishment (execution) on Khalid because it was not willful transgression.
According to Shiite view, Khalid Ibn Walid was not a good Muslim.
Prophet sent Malik ibn Nuwayra to collect alms taxes. However, before he could returned, the prophet (p.b.u.h.) had already passed away. Upon learning that Abu-Bakr hold the the title of caliph instead of Ali illegitimately, he denied to give the taxes to Abu Bakr. Khalid ibn Walid was sent and he killed him and within the same day, he slept with his wife, which is a grave sin according to Qur'an and common Islamic jurisprudence.
The wives of men who have died must observe a waiting period of four months and ten days; [Al Baqara:234]
Personality of a person should be checked completely from Islamic perspective rather than for a specific time and military commander abilities. This can be inferred from this verse regarding hypocrites :
And whoever of you reverts from his religion [to disbelief] and dies while he is a disbeliever – for those, their deeds have become worthless in this world and the Hereafter, and those are the companions of the Fire.
Malik ibn Nuwaiyra was a Muslim and not an apostate , which he confirmed by saying shahada during his death moments.