I have read somewhere that Duryodhana's real name was Suyodhana and later he was named Duryodhana after his deeds. Their logic was su= good and dur=bad( though I am skeptic about this). Regardless, was Duryodhana intially known as Suyodhana?
The meaning given by you is wrong. DURYODHANA means who is difficult (Dur) to be vanquished in battle(yodhana). Names of Kauravas narrated by Vaisampayana.
Janamejaya said, 'Please recite the names of Dhritarashtra's sons according to the order of their birth.'
"Vaisampayana said, 'Their names, O king, according to the order of birth, are Duryodhana, Yuyutsu, Duhsasana, Duhsaha, Duhsala, Jalasandha, Sama, Saha, Vinda and Anuvinda, Durdharsha, Suvahu, Dushpradharshana, Durmarshana and Durmukha, Dushkarna, and Karna;
So, Duryodhana from his birth was known as Duryodhana.
A verse found in Virāṭa Parva of the Mahābhārata suggests that Duryodhana (meaning, one who is difficult to fight with) was the former/given name of the Duryodhana and Suyodhana (easy to be fought) was acquired later.
18 moghaṃ tavedaṃ bhuvi nāmadheyaṃ; duryodhanetīha kṛtaṃ purastāt
na hīha duryodhanatā tavāsti; palāyamānasya raṇaṃ vihāya
Renounce your deeds and great fame. Why are you running away in this way and refraining from battle? Why aren't trumpets being sounded for you now, the way they were sounded when you set out to do battle? I obediently follow Yudhishthira's instructions. I am the third of the Parthas and I am steadfast in battle. Therefore, turn around and show me your face. O son of Dhritarashtra! Remember how Indras among men are supposed to act. You have been named Duryodhana earlier, but that name will be uttered on earth in vain.194 There is no Duryodhana left in you. You are running away and refraining from battle. I do not see anyone to protect Duryodhana, either at the front or at the back. O foremost among Kurus! Therefore, run away from the battle. Protect your beloved life from the Pandava.
194 Duryodhana means someone who it is difficult to fight with.
For more in-depth analysis check these tweets from Nityānanda Miśra and True Indology.