It's impossible to judge light levels from photos alone, mobile phones really hike up the exposure in low light these days. The room always was brighter than it seemed. It might be too bright and I agree less is more, there was a reason a lot of Hex's detailing was very dim in the queue, but I've not been in person so impossible to say.
I dont think wood's glass was used in the haunted house, they deliberately used easily obtainable, standard parts for its original light units so they could be cheaply replaced and still look good. Of course even with ease of maintenance built in, proper show maintenance was still so poor over the years.
Merlin introduced a global policy of replacing all lights with LED bulbs in a bid to save energy (read: money), which anyone with an understanding of lighting would know such a scheme would need an incredible amount of consideration and strategy to retrofit attractions from the 90s with LED. All the circuits run off voltage dimmers or dimmer circuits to get a very natural flicker effect. These circuits have worked for the last 25 years.
Unfortunately Merlin's strategy was to just get cheap electricians to go around and match colours (UV looks blue if you're ignorant enough s'pose) and stick LED bulbs in and be done with it, or replace original units with cheap LED units. Just look at what this did to Tomb Blaster, Vampire and BubbleWorks in its final year. The LEDs lit everything up like an office room, no atmosphere at all, faulty strobing effects instead of a natural flicker/ambiance, and horrible digital colour.
It would be very easy I think to give Duel proper scenic lighting again, either that or it should have been professionally redesigned to recreate the original lighting effects using correctly dimmed LEDs - but nothing can replace the look of proper filtered spotlighting and real, subtle UV lighting.
Also, as has been pointed out, true UV does not actually exist using LED. UV does not mean "purple", it means no visible light, with only the UV pigments in the sets and monsters highlighted out from the darkness. Terrible that this was completely overlooked, when so many of the Haunted House's intended effects relied on true blacklight.