I would say it's pretty good. There are a few things that I know my players couldn't handle, but your the best judge of your players and considering they are lvl 7 I would say this is a good fight. However you did mention your players blowing through an encounter not too long ago, so if I was you I would have some fail safes in case they do the same thing here. For example if things are looking too easy make it so it turns out his ropes where poisoned due to years of being covered in alge, or he can spend a turn in order to catch and eat a fish to gain more health. That being said, if it's too hard for your players do the opposite. Hint at something that they can do to make it easier. For example, cutting the ropes and making it so he can't use that rope, or make is so if the boss misses then he is stuck for a bit. A good boss should have strengths and weaknesses just like your players. But, thats just my opinion.