Yes, its right to say that Ram was only a human being. The boons that made Ravana invincible made it mandatory for Lord Vishnu to incarnate in a simple human form, without any miraculous abilities. Otherwise it would’ve been impossible to slay Ravana.
However, this does not mean that Ram had no link with Lord Vishnu. Ram definitely was an incarnation of Lord Vishnu and the link between the two has been made obvious at several occasions in Valmiki’s Ramayana. Some of the evidences from the book are depicted here:
Evidence 2: While fighting with the son of Ravana (Indrajit), both Ram and Laxman are rendered unconscious by the serpentine weapons used on them by Indrajit. Indrajit breaks the code of the warrior by using magic and turning invisible; and shoots a net like weapon made up of snakes on both Ram and Laxman, thereby capturing them. The monkey army tries to fight back, but they were unable to locate the invisible Indrajit in the darkness of the night, and thus the army loses all hope of victory (Yuddha Kanda – Sarga 44, 45). Indrajit assumed that he had killed off his enemies as it was impossible for a human to escape the snake weapon and heads back to his palace. While the monkey army sits dejected and hopeless, the mystical king of birds Garuda (the vehicle of Lord Vishnu) appears on the battlefield to everyone’s surprise. All the snakes binding Ram and Laxman flee when they see the giant eagle. Garuda heals both brothers with a single touch and also doubles their vitality. Both Ram and Laxman are surprised and they ask Garuda for an introduction. Garuda in response says that Ram should consider Garuda as a close friend, as close as his very breath. He then further explains the nature of the weapons used by Indrajit and finally embraces the brothers before heading out (Yuddha Kanda – Sarga 50). Garuda, the private vehicle of Lord Vishnu, made an appearance in the middle of an ongoing war, just to heal two random humans within an army of monkeys, only goes to show the strong link between Ram and Vishnu.
However, this does not mean that Ram had no link with Lord Vishnu. Ram definitely was an incarnation of Lord Vishnu and the link between the two has been made obvious at several occasions in Valmiki’s Ramayana. Some of the evidences from the book are depicted here:
Evidence 1: In Bala Kanda – Sarga 16, Lord Vishnu agrees to incarnate in the human form and chooses king Dashratha as his father. At that point, King Dashratha was already in the process of performing the Ashwamedh sacrifice, in order to beget children. After the sacrifice is complete, the celestial being Yana Purusha appears in front of King Dashratha from the sacrificial fire and offers him a divine sweet dessert, which was basically a medium through which Lord Vishnu would incarnate (Bala Kanda – Sarga 16). King Dashratha distributed the dish amongst his wives. He gave 50% of the dish to Kausalya, 25% to Sumitra, 12.5% to Kaikeyi and the remaining 12.5% again to Sumitra. Thus, Sumitra got the dish twice and gave birth to two sons namely Laxman and Shatrughan (Bala Kanda – Sarga 18). So, all four brothers were born with a portion of Lord Vishnu within them.

Evidence 3: While fighting head on with Ravana, Laxman was mortally wounded when the Brahma Spear (absolute weapon of destruction) was used on him. For some miraculous reason, Laxman does not lose his life. Seeing him still alive, Ravana springs forth and grabs Laxman and tries to lift him up. With the strength of thousands of elephants, Ravana had the ability to lift the three great mountains namely Himavat, Mandara and Meru. But despite using all his strength, Ravana was unable to lift Laxman (Yuddha Kanda – Sarga 59 – Verse 111). With the weapon of Brahma still impaled in his chest, Laxman gets a premonition of sorts, making him realize that he is in fact a part of Lord Vishnu (Yuddha Kanda – Sarga 59 – Verse 112). Hanuman steps in with the intention to help Laxman and temporarily incapacitates Ravana by punching him in the chest. Hanuman then thinks of carrying Laxman away from the battlefield in order to save his life. Judging by how greatly Ravana struggled to lift Laxman, but was unable to even move him, Hanuman should've had a hard time lifting Laxman and carrying him away from the battlefield. Instead, he lifts Laxman and is surprised to find that Laxman feels as light as a feather to him, probably because of his friendship, love and devotion for Laxman. Hanuman carries Laxman to safety and as soon as the Brahma weapon is removed from Laxman’s body with medicinal herbs applied on his chest, Laxman gets back on his feet and is completely healed. The spear of Brahma, the creator of the universe, was unable to take the life of Laxman, thus proving that Laxman definitely had some divine connection. Please note that this battle should not be confused with the one where Laxman was fatally wounded by Indrajit and was saved by the Sanjeevani herbs brought by Hanuman (Yuddha Kanda – Sarga 101).
Evidence 4: After defeating Ravana in battle, Ram subjects Sita to a trial by fire. At that point, several celestials appear at Lanka to meet Ram. The celestials included Kubera (king of Yakshas), Yama (god of Death), Indra (Lord of the celestials), Varuna (Lord of the waters), the illustrious three eyed Lord Shiva (the lord of all gods), Lord Brahma (the creator of the universe) and the spirit of Ram's deceased father king Dashrath. These celestials then ask Ram why he is not able to recognise himself and Sita despite his divinity. Ram is surprised at this and asks the reason for their question. Lord Brahma then formally identifies Ram with Lord Narayana, the wielder of the divine disc in great detail (Yuddha Kanda – Sarga 117). Lord Brahma also states that Sita was no other that the divine goddess Lakshmi, incarnated as a human. This is the most prominent evidence in the great book Ramayana that Ram was an incarnation of Lord Vishnu.
Many people claim that there is absolutely no account of Rama's divinity in the entire Ramayana. Please feel free to share this post with such individuals. The divine connection could not have been made more obvious by Valmiki and the account of this has to be brought to light.