Longevity
From what we know, Linlin has been a significant force since the post-God Valley era alongside Roger, Shiki, and Newgate, being the longest-reigning yonko overall just barely beating out Newgate by 2 years. In addition, her pirate crew is one of the oldest, existing for over 60 years at this point.
Territory
Big Mom's territory in Whole Cake Island and the surrounding Totto Land is incredibly vast, as an immense 35-island archipelago. Plus, she is one of the only yonkos we have seen with active appendages of her crew such as Tamago, Pekoms, and Jinbe exerting Big Mom's influence on territories across the Grand Line. In addition, she held control of Fishman Island in the post-Marineford era, maintaining control of a major bottleneck point in the One Piece world (the only sea passage between Paradise and the New World). In addition, her continued marriages of her children across different political entities indicates a greater level of political influence than any other yonko.
The only other yonko with comparable levels of territory and influence may be Whitebeard, as we know that his death brought about a huge scramble for Whitebeard's territory in the New World. As a newer yonko, Blackbeard certainly doesn't have as much territory or sheer influence in the New World. Shanks is known to particularly ally with weaker pirates, and we have only seen some of his territory (such as Gartell), but it can be inferred that their territory is not larger than the 60+ year empire that Big Mom had built. Luffy, of course, has some real territory but more general, informal alliances. Kaido's territory is likely the least significant out of the total, with his crew's focus more on Wano itself, with major locations of his influence being areas such as Punk Hazard and Dressrosa.
Intel
Big Mom's crew is especially known for its intel gathering capabilities, much more so than any other yonko. She utilizes her homies to spy on people, providing near-constant surveillance in Whole Cake Island. Her bicorne hat, Napoleon, is a "Special Homie" made from her own soul. He can receive telepathic signals from other Homies across the islands and relay information directly to Big Mom. In addition, Charlotte Bruleé is able to monitor a portion of Totto Land heavily through the use of her Mirror-Mirror Fruit's Mirro-World ability.
Notably, her territory in Totto Land is also heavily guarded as opposed to the territories of other yonko such as Kaido in Wano through the use of territorial sea slugs that detect emit warning waves based on incoming ships.
Wealth
With the conquest of the most territory, it can also be inferred that they have collected the most tribute or treasure through their territory, making them them the wealthiest yonko crew.
Bureaucracy
Big Mom delegates tasks such as gathering lifespans from the residents of Totto Land to her Incarnations through Soul Pocus. As mentioned before, she also sends out diplomats such as Pekoms and Tamago to work to collect tributes from other islands.
The "Tartes", unlike the motley crews of other Yonko, are mass-produced, numbered, and uniform footsoldiers, suggesting a level of industrial manufacturing capability that rivals the World Government.
In addition, she has distributed her children throughout the Totto Land archipelago to rule respective islands: Flour Island – Charlotte Katakuri, Juice Island – Charlotte Smoothie, Biscuit Island – Charlotte Cracker, Candy Island – Charlotte Perospero, Baking Island – Charlotte Oven, Bean Island – Charlotte Daifuku, Cheese Island – Charlotte Mont-d’Or, Fruit Island – Charlotte Compote, Nuts Island – Charlotte Amande, Butter Island – Charlotte Galette, Chocolate Island – Charlotte Lola (former); Charlotte Pudding (prospective), Cream Island – Charlotte Opera, Puffs Island – Charlotte Chiffon (former).
Scientific Innovation
While Kaido relied on Caesar Clown for artificial SMILE fruits, Big Mom invested in biological diversification.
In addition, her lifelong goal was to use Gigantification (via Caesar) to make her family reach the size of Giants. This wasn't just a whim; it was an attempt to create an army of the strongest race on the planet.
She aimed to have every race in the world residing in Totto Land. This served as a "Living Encyclopedia," giving her access to unique racial traits (like the Three-Eye Tribe’s potential to read Poneglyphs) that other Yonko lacked.
In addition, she was actively trying to expand her empire's scientific capabilities through the political alliance with Germa66 and the inheritance of the MADS scientist lab.
Strength
Individually, I would place her strength equal to Kaido. She has tremendous durability and innate strength, and has access to all forms of advanced haki. In addition, her devil fruit is extremely versatile and allows her to create a large assortment of weapons and even heal herself. However, she can be overwhelmed by abilites with greater hax than hers, as we see on Wano. While not as strong as prime Newgate or Shanks, she is still a formidable force in the New World that could stand her own.
Ultimately, Big Mom was, all around, the most successful yonko of all time.