Was Balram more powerful than Jarasandha, Bheem and Duryodhan?

There were only four people so absurdly powerful in those days: Balram, Jarasandha, Bheem and Duryodhan. And Balram was the most powerful of all these. In the traditions surrounding the Mahabharata and related texts, he is generally considered one of the most physically powerful warriors.

Balarama is regarded as an incarnation of the serpent deity Shesha. Not only was he a warrior with immense physical strength, he was also the teacher of mace fighting (gada-yuddha) to both Bhima and Duryodhana.

Compared with Bheem

Bheema is famous for tremendous strength and ultimately defeats Jarasandha and Duryodhana.

However, Bheema learned mace fighting from Balarama. Balarama himself believed Duryodhana had better technical skill, while Bheema had greater raw power

Still, Balarama was usually seen as above both of them in mastery.

Compared with Jarasandha

Jarasandha was extremely powerful and fought Bhima for 27 days before dying. But Balarama was a divine being and had legendary strength and weapons like the plough (hala). So in most interpretations, Balarama was stronger than Jarasandha.

Compared with Duryodhana

Duryodhana was a very skilled mace fighter and personally trained by Balarama. But he was still a student, so Balarama was considered superior.

In Drona parva, Krishna narrates an incident where Balarama countered Jarasandha

''Jarasandha was angered, incited by Rohini's son.To kill us, he hurled a club that was red at the tip. It was as resplendent as the fire and it divided the sky, like a parting." It was seen to descend, like the vajra released by Shakra. On seeing that the club was descending, Rohini's son wished to counter it and released the weapon known as sthunakarna. Countered by the force of that weapon, the club fell down on the ground. It shattered the goddess earth and made the mountains tremble. There was a terrible rakshasi named Jara and she possessed great valour. O scorcher of enemies! She united the infant and it came to be known as Jarasandha. Two separate parts were born from the bodies of two separate mothers. Since she united them, he came to be known as Jarasandha. O Partha! That rakshasi was slain by the club and the weapon known as sthunakarna and entered the earth, together with her son and kin. O Dhananjaya! Jarasandha was deprived of the club in the great battle and while you watched, was killed by Bhimasena.''

-1133 (156), Drona Vadha parva, Mahabharata.

Balarama with his weapon Sthunakarna not only countered Jarasandha's powerful mace, but also killed Jara rakshasi and her son and relatives. This was how powerful Balarama was.

Krishna (and Balaram) didn't kill Jarasandha to respect Brahma's will.

''And the lord Shouri, supreme among strong ones, with a valour equal to that of tigers, also remembered. This did the truthful Achyuta remember. It had been destined that Jarasandha would be killed by the valorous Bhima. Madhusudana, the younger brother of Haladhara, foremost among those who have controlled themselves, wished to show respect to Brahma and did not wish to kill him himself.''

-245 (20), Jarasandha vadha parva, Mahabharata.

''And the lord Shouri, supreme among strong ones, with a valour equal to that of tigers, also remembered. This did the truthful Achyuta remember. It had been destined that Jarasandha would be killed by the valorous Bhima. Madhusudana, the younger brother of Haladhara, foremost among those who have controlled themselves, wished to show respect to Brahma and did not wish to kill him himself.''

-245 (20), Jarasandha vadha parva, Mahabharata.

Why Balarama did not participate in the war

During the Kurukshetra War, Balarama chose to remain neutral because Bhima and Duryodhana were both his students and he did not want to fight against either side. Moreover, he didn't want to oppose Krishna. So the best option for him was to stay away from both sides.