Manilla type Mangos in SoCal often have smaller nubbin fruit the first couple years of fruiting before they start producing full sized fruit. The nubbins usually have incomplete pollination and have either no seed or a very small seed. The flesh from nubbins is very sweet because the fruit is very small so more minerals and photosynthates can be put towards that fruit.
The larger fruit is a good thing although they will likely be less sweet. I’ve found the Manilla type Mangos to be relatively mediocre in quality when you compare it to some of the varieties we often talk about on this forum. I used to love manilla Mangos until I had Lemon Zest, Sweet Tart, Coconut Cream, Peach Cobbler, Pineapple Pleasure, Kesar, Fruit Punch, E4, M4 and many others.
If you love the fruit, that’s all that matters but I would recommend trying your hand at top working a few branches with Sweet Tart, Venus or Kathy for example.
Simon