Holy cow, what a shame 7 years and this is what you have with your mango tree. In Burbank, you have much more heat than I in Huntington Beach but my oldest mango Trees (5years) have a much stronger and robust lower rootstock with relatively healthy growth (at least by California standards). Here are the four golden rules I came up with over time if you want to have success in SoCal growing mango trees.
1. Grow in sandy soil. Mango trees do poorly long-term in heavier clay-type soils. The smaller feeder roots need to spread out laterally and this is more challenging in heavier soils found in many parts of SoCal.
2. Do not use Florida Turpentine rootstock in California if possible. Mango seedling trees work best (for later grafting) but not all seedling trees are vigorous growers. Out of 10 seedlings trees, 3-4 will be excellent for rootstock. I use Ataulfo Seeds from Mexican yellow mangos I buy at the store. Germinate 10 seeds and after 1-2 years plant the top 3-4 growers. You can also get Poly seeds from Florida and do the same thing as both methods should work well.
3. When Grafting scions to the mango lower rootstock select faster and more vigorous varieties that do best in our marginal climate. Cac, Seacrest, Peach Cobbler, Lemon Zest, Guava, 0-15, and Buttercream are some examples of fast growers at my location. Sweet Tart, Val-Carrie, Mallika, Nam Doc Mai, and Angie are examples of moderately vigorous varieties that seem to do well at my location but they grow slower than the first group in general.
4. Plant your mango trees South facing with full sun and no blockage from other trees or man-made obstacles. Maximum heat and Sun are some of the keys to long-term success. Roots need space and oxygen for healthy growth. Avoid planting mango trees near cement or bricks that block nutrient intake from above.
Good Luck
Johnny