What does Jethuun have to do in order to steal a power? Does that require physical touch? Macai's power is natural, he is a firebender and was therefore born with it. He initially controlled average orange and yellow flames like most firebenders and worked hard to achieve white fire by having nearly perfect bending form. Bending is in the breath, it has little to do with vision hence why Toph was one of the greatest earthbenders of all time.
Maximum potential bending for Macai in a normal sense is during Ozai's comet. Which could be enough to destroy a city but not in one blow. It would be slightly below comet Ozai's output since Ozai had the largest flames and the most vitality when it came to firebending. It would probably be more like Azula and Zuko's output when they fought in book 3 of ATLA except with white fire instead of blue or normal. Macai's power is not just due to his physical ability, much of it is due to his skill, discipline, and tactics.
If a random person gained his powers, they likely would not be as dangerous or effective as him. With that being said, Macai's powers along would be enough to be a force. Would stealing Macai's powers take away his abilities or would it simply cause Jethuun to have Macai's powers too?
Macai doesn't have to trade with that monster either, if he mainly fights melee Macai could use rocket propulsion to fly over him and bombard him into submission. Dante on the other hand, sounds more like a master strategist. What are all his powers, you said lasers but it looks like he can generate lightning as well and use it to dash around.
Dante looks like a more capable straight up fighter than you seem to describe. Also, what kind of people does he normally fight. How smart and experienced are these opponents? Macai has fought in the Hundred Year War for a two years by the time of its end. He's been up against a lot of officers and leaders more experienced than him and he still outsmarted them. He directly draws from people like his father (a war general and prudent strategist) which means he won't be easy to outsmart.
Macai himself is a tactical expert, in a battle vs battle sense or within the first few engagements he can be even less predictable, more overwhelming, and harder to deal with than Azula herself. The same Azula who staged a coup in Ba Sing Se, the capital of the Earth Kingdom at the age of 14. Macai is a year older than her but has similarly spectactular feats (again not in terms of some grand coup but more in the form of winning many difficult battles despite various variables).
When it comes to skills, from what I am guaging Macai would be a much better straight up fighter. He probably has a lot more experience in duels and 1 vs 1s. Macai also is used to fighting other people with powers but not Dante's specific set of abilities (in his universe most people have the same set of fire, water, or earth powers).Dante's best chance against Macai in a fight is utilizing his unique abilities which Macai would not be as familiar with.
When it comes to fighting style, it is much easier to figure out Macai's physical fighting style than his bending style. Macai's bending style incorporates a massive utility of powers and moves. Macai has been training since he was a child and a fighter has to be fully focused against him in a fight to not immediately lose. Macai also has white flames that are blinding and directly looking at his attacks can cause an opponent to be temporairly blinded.
When it comes to bending, Macai's style can be hard to discern at times. When it comes to hand-to-hand he is not as tricky and has a more straightforward style but Macai can mix his bending with his physical attacks and could potentially lure your hero into a counter or trap by doing that and intentionally looking to be predictable.
To beat Macai, a fighter should have a combination of strategic/tactical sense as well as a natural ability to fight. The natural fight ability is not just like a science but must be intuitive and natural. It can develop over time with experience, but fighting really isn't a science. It's more of an art. Overthinking all the time isn't the answer at the highest level but pure brawling won't even get someone to the mid tier.
If Duante is too focused in his plan, I don't think he'll beat Macai. The trick in fiction to beating a great planner is by being a decent planner and being erratic (we see this with Thrawn in Star Wars as well as other characters). Duante needs to be smart as he is, but he also has be raw and adaptive on the spot.
In Macai's universe, fighters with these abilities are Ozai, Iroh, and Zerrel who are all capable of beating him though some would argue that Ozai and Iroh are somewhat buffed in the AMJ verse so keep that in mind.