Yeah, see no.
I can go with the idea the guy may have been a former bender, but see by saying he's energy bending still kills the Equalist movement. It undermines it and makes the whole thing convoluted. It would just be bad writing. The Equalist movement is an interesting dynamic.
Energybending is a specific thing, it took Aang's energy as a bender to do it.
Energy blocking is a different animal that can have the same outcome.
I think being an Equalist is actually an important plot point. The land is developing and what was a running joke when Sokka was the brunt of it - he was a non bender, worthless. So Chi Blocking actually helps level the playing field between non benders and benders. Now people who can't bend can match up to a bender and one that permanently blocks the power is scary and to be feared. It shouldn't have to be about "Energy Bending" - only in the sense that it may have been the learning point for a non bender to use the technique in a non bending fashion.
I think putting it off as simply Energy Bending undermines the whole problem that a non bender has with benders feeling unequal.
I do think Yakone and Amon's stories are related.
This is my theory. Aang was in his 40's with the Yakone incident (least that's what it looked like to me), and Aang died at 66 years of age. I think the firebender that scarred Amon may have been Yakone. It would put him at the right age. I believe he's younger than Tenzin. He's definitely older than Korra. It would put Tenzin at the right age as to why he remembers the incident.
I really see no reason Amon would lie about the incident of being burned. I think it's a strong reason for him to seek change. It's like "Batman"
Tenzin is 51 and the youngest, Kya is the oldest iirc, and Bumi is brother is a non bender. Aang died when Tenzin was 34-35 years of age. Minus 20 years and he'd be about 15 during Yakone's time.
Pema is 35
They mentioned the Yakone incident happend 40 years ago, which would put Tenzin at 11, but if it's an approximation he may have been older (as I said 15)
If Amon is in his 40's he could have been about 5 years old with Yakone around, and I think that would put him at the ripe age for a traumatic incident that would have changed him. I think he may have been one of Yakone's victims.