Shalya respect thread.

He is the character who Krishna considers superior to his own three students (Krishna was “Parshuram” in a previous life):

“I think that the ruler of the Madras is in battle equal to Bhishma or Drona or Karna, or perhaps, superior to them. I do not, O ruler of men, even upon reflection, find the warrior who may be a match for Shalya while engaged in fight.”

Shalya Parva: Section 7

Anyways Krishna may have either been lying or telling the truth but the fact is that he held Shalya in a high regard, believed him to be a very powerful warrior.

He was an all rounder, one of the few supreme mace fighters in the epic. His encounters with Bhima prove this fact.

Incident 1 (11th day)

“Struck by the ruler of Madras with his mace on both the left and the right side, Bhima moved not in the least, like a hill riven by the thunder. Similarly, the mighty ruler of Madras, struck by Bhima with his mace, patiently stood still like a hill struck with the thunder. Both of them, with upraised maces, endued as they were with great impetus, fell upon each other, coursing in shorter circles. Quickly nearing each other, then by eight steps and falling upon each other like two elephants, they suddenly struck each other with those maces of theirs made entirely or iron. And each of those heroes, in consequence of the other's impetuosity and violence being struck with each other's mace, fell down at the same instant of time like a couple of Indra's poles.”

Note that both him and Bhima became unconscious, think about how much physical strength Shalya would have.

Drona Parva: Dronabhisheka Parva: Section XV

Incident 2 (18th day)

“The noise made by the blows of the maces of those two lions among men was heard on all sides like successive peals of thunder. Having ceased for a moment, those two warriors of great energy once more began, with uplifted maces, to career in closer circles. Once more the clash took place between those two warriors of superhuman feats, each having advanced towards the other by eight steps, and each assailing the other with his uplifted iron club. Then, wishing to get at each other, they once more careered in circles. Both accomplished (in the use of the mace) they began to display their superiority of skill. Uplifting their terrible weapons, they then again struck each other like mountains striking each other with their crests at the time of an earthquake. Exceedingly crushed with each other's mace in consequence of each other's strength, both those heroes fell down at the same timelike a couple of poles set up for Indra's worship.”

Shalya Parva: Section 12