At the start of the plot. Vernon is weak, marginally better at fighting than your average joe, little to no desire to engage in combat, his only fighting ability is his above average dexterity and fast mind.
At the end of season 1 Vernon is a competent fighter able to hold his own against mutiple foes and even able to stand against some strong ass opponents... including a dragon.... He is still a reluctant fighter, but won't hesistate to dish some pain.
At the mid point of the plot Vernon can fight off dragons plural, and his powers rival that of some of the strongest characters in the entire world, even going so far as to challenge some of the mightest beings on the planet, the elder dragons...
At the end of the plot...We are dealing with a 1,63m guy that can split the entire world in half, Like the world friendliest but slightly depressed nuclear warhead
As I mentioned above, Vernon's streght lies in his agility, he develops a combat style that 'needs no strenght' as he progresses and slowly focuses on increasing his stamina and resilience to be able to complete with might and tough beings of the world of JTA.
His magic is flat out OP in theory, he can create an aura an manipulate things inside it using a sort 'telekinetic like' power which grants him a lot of flexibility in combat, he can also create copies of objects he interacts with but copies do not last forever and use up a ton of energy, so it is usually best for him to already have materials in hands as he can bend materials to his will... For instance... If he has metal he can instantly forge a sword of that metal (albeit it will slowly go back to it's original shape over an hour),
His combat style revolves aroudn a clever use of things he has in hand as well as the enviroment to get an advantage, unlike other mages who can just create fireballs and melt cities, he is very much a 'tactician' type hero, but don't worry... there are plenty of people to challenge the little guy.
Also, I do not believe he could beat goku... Maybe in his most powerful form yes, but that is still kind of a long shot.