When we say that a Mitzva is Mesugal for something that is very different from a Segula in the more widely used form. While not every Mitzva has a benefit on this world, many Mitzvos have by products that benefit us on this world. The by product does not necessarily make it a ‘better’ Mitzva.
There is a Machlokes Tana’im if you may prepare for a Bris on Shabbos those things that could have been prepared beforehand. Rebbi Eliezer hold that you may and the Chachamim argue. Naturally, we Pasken like the Chachamim andwe may not prepare on Shabbos. In Rebbi Eliezer’s town they Pasken like him, as is often the case. The Gemara says that in that town, in Zechus of their extra effort in Mila they died in their time, they lived long.
Obviously, that was not meant to say that those people are more right. If people in other villages would prepare for the Mila on Shabbos they would be punished. However, diligence in Mila has it’s benefits and they gained from the fact that they happened to have to follow Rebbi Eliezer’s rule.
It is silly to match Mitzvos and to trumpet a certain Mitzva as the main one. Tzeddaka is great and has it’s own by product. It also doubles as a very popular Mitzva that even non-Jews appriciate. By their yardstick it is definitely the only important Mitzva. Make sure to use our yardstick, in which one Mitzva doesn’t outpace another.