yeah, so for me it really depends on what you are doing and where.
quick fun fact
The high quality backup lights have more light output than a 10w HID. This was enough for a primary light up until very recently, and realistically still is enough light for most people in most situations. If I was doing intro level dives, I would have 0 issues using a high quality backup light as my primary. I would likely carry 4 lights in this situation, 1 primary for the way in, 1 primary for the way out, and 2 proper backups. I would do this long before I went to something like the Light Monkey lights or the Dive Rite LX20. For the cost, the performance is close enough, and the convenience is quite nice.
@stuartv mentioned the Sola 800 vs the DGX600 and it's run time, but the DGX600 will dim over the burn, so yeah it is burning for however many hours longer, but it's not putting out the same light as it was in the beginning. This is good enough for most people, but my backup lights are all multiple light outputs so I can get about an hour of burn on proper high, or I can get however many hours of burn time at a low light level to get out of a cave. That is VERY nice to have.
Now, I think these lights are sufficient for most wreck diving because the duration is a lot shorter than many cave dives in the part where you actually need the light. You don't need lights to function at full power for descent, ascent, deco, etc, so something convenient to turn on and off is nice which removes twisty's for me.
R105T HANDHELD DIVE LIGHT-Technical-A Lighter Ocean with Ano Dive Lights
That is currently the backup light that I'd recommend since Securitying removed the one that I liked from Amazon for some reason. Unsure on why, but
@stuartv had bad luck with one due to a sharp edge cutting the bolt snap line.
Realistically, you have to figure out what kind of light you need and why. Do you need eleventysevenmillion lumens to light up the whole ship? Maybe, if you're diving and it's bright out, you need more light to clear shadows than you do at night, but you may not want that. The canister lights still have a very good justification, and the UWLD baby canister is selling like hotcakes for the wreck divers because of how small it is and how powerful the lights are