To be honest, my previous complaints about how difficult I found NG+ have pretty much evaporated since my last post.
The short answer was one word: Practice.
In more detail my timing and sense of spatial awareness was off so I was constantly jumping into situations where Bats was in danger of taking damage if my execution of a special move was off. With practice I've gotten a lot better at hitting the effective special for whatever the situation demands, and I'm now I'm a lot more aware of what's going on around me.
On Normal difficulty you can get away with being sloppy, on NG+ and the harder Riddler's revenge combat scenario's you simply cannot.
Also, learning how the various gadgets are set to prioritize particular targets is massive. For example REC quickfire will always go to Abramovici/Stun-Rod dudes/Shield dudes if they are in the field of view, even if a machete-wielding thug is right in your face.
What tended to mess me up -particularly true in the gladiator pit fight, which was raping me- was that as fights against large numbers of thugs progressed the balance of enemy types changed and I wasn't adjusting my strategy to compensate. Towards the end, because I was missing weapon-breaks I'd be facing fewer enemies but a higher number were armed with clubs and blades making them generally more able to hit me a longer range.
To be honest I'm not at the stage yet where I'm getting 3 medals on every combat challenge, but I'm now 2 medalling most reliably, and I feel comfortable that I can and will improve further.
Its been very rewarding to push through and elevate my performance, even if it has been frustrating at times.
My advice to anyone who's gotten stuck, is to persevere but don't expect miracles to happen in the space of a single play session. Come back, a day later and you will see real improvement if you have observed and internalized your mistakes. There is a distinct rhythm to combat, so you can't really push through, you just need to make fewer mistakes and be able to execute the right move for the given situation.