When Hit and Goku first fought, Hit managed to have the edge on Super Saiyan Blue + Kaioken * 10 Goku. However, when they had a rematch, Super Saiyan Blue Goku was strong enough to overwhelm Hit and end the match as a Draw. Does this mean Super Saiyan Blue Goku became 10 times stronger after the Goku black arc or did Hit get weaker?
There's a comment misinterpretation made by a lot of people with regard to Hit in terms of power. While Hit is a very strong character and in terms of raw power is only second to Kefla in Universe 6, at the same time, Hit does not have the same level of raw power and toughness displayed by characters like SSJB Goku, SSJB Vegeta, Golden Freiza, and Base Toppo (Note: Jiren is way too strong to be compared to Hit). At the same time, Hit is considered to be a Legendary Assasin who is 1000's of years old and also an experienced Martial artist.
Unlike the previous series, Dragon Ball Super has laid emphasis on other factors such as strategy and technique, rather than pure power.
- One good example for the same is in ROF arc where Golden Freiza has the upper-hand in terms of Raw power but ends up losing to Goku on account of his strategy where he managed to tire Freiza.
- If you watch the fight between Hit and SSJB Vegeta, Hit clearly overwhelms SSJB Vegeta without even fighting seriously. Base Goku on the other hand, catches Hit off guard and lands a few blows on him and forces him to fight seriously. This obviously doesn't imply Base Goku is stronger than SSJB Vegeta. Goku managed to figure out Hit's timeskip and counter it
- When SSJB Goku began to overwhelm Hit and he powered up, Goku stated that Hit's attacks hadn't become stronger. However, Hit managed to increase the speed of his time skip and made it impossible for Goku to counter.
- Goku Hence required to use SSJB + Kaioken * 10 to outspeed Hit and knock him out. Before Goku uses his final blow on Hit, Hit stated that he managed to increase the speed of his timeskip again and evade Goku's attack. Hit never really used a powerful attack of his own or took the attack head on and Got back up, like Jiren, Goku, Vegeta, Toppo and Freiza.
A part of your questions asks whether Hit got weaker. This is a definite no. We know this as Goku himself stated that Hit was a lot stronger compared to the Hit in the Universe 6 vs 7. This was because he was free to use his assassination techniques which he couldn't use in the Universe 6 vs 7 tournament on account of the rules. In this match, you can see Goku barely lands any attacks on Hit as he mainly uses stealth throughout the course of the fight and hides in a different dimension spawning clones and was landing on heavy blows on Goku(He even landed a punch on Goku which more or less Killed him). Goku on the other hand, managed to end the match as a stalemate landing 1 power Kamehameha by breaking through Hits personal dimension. This shows Goku's raw power being superior to Hit.
- Even in the tournament of power, when Dyspo managed to counter Hit and land blows on him, Hit was heavily injured. At the same time, Dyspo's punches barely did anything to Goku and even Freiza was barely damaged by Dyspo(Dyspo managed to overwhelm Freiza only because of his speed, not superior in terms of raw power).
- Hit was completely down after taking a single eye attack from Jiren while Goku had no visible damage and managed to get back up easily and fire a Spirit Bomb at Jiren.
Goku did get a lot stronger after the Goku Black arc but no way to conclude whether he got 10 times stronger since power levels do not exist anymore. However, Hit in terms of Raw Power isn't significantly strong. Even Gohan at full power and Android 17 would be able to fight Hit(Solely in terms of Raw Power), based on their performances in the tournament of power. As far as technique and experience goes, Hit is on a whole another level and even the more experienced fighters like Goku and Vegeta would have trouble against Hits special techniques forcing them to use Raw power with a strategy to try to overwhelm Hit(Another good example of the same is where an exhausted Base Goku begins to overwhelm Super Saiyan 2 Caulifla on account of having more experience and being a better Martial Artist).