As far as I understand this is what Shanks trying to imply in that panel " You know that I am strong and I wasn't being careless yet he did this to me." According to Shanks BB has great potential and he isn't someone that can be underestimated. He implied that Ace at his current level can't deal with BB which is why he requested WB to stop Ace. He even know that BB would someday come after WB's head( that Shanks.
).BB is a lot stronger than many of us think, it's just his carefree nature that makes him look like a weak dude. It took just one hit for him to inflect considerable damage on Luffy on the other hand Ace pushed BB to his limits despite of being at a huge disadvantage.
Obviously he has gotten stronger.There are a few points that should be taken into consideration before deciding how strong he has gotten.
1. First and the most important point would be his growth rate is nowhere near to that of Luffy/ Ace.
2.Unlike Luffy and Co he has no need to rush to get stronger .
3.He received fatal physical wounds from Akainu so he need some rest.
4.Luffy spent most of his time to get stronger but Jimbe has no reason to do so.
Taking all these points into consideration he didn't get much stronger when compared to pre-TS Jimbe. Pre-TS Jimbe was most likely weaker than Ace which means that Ace is more or less on par with current Luffy.
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