Behl, that could be one of the factors affecting the growth. We have noticed that vigorous varieties such as Valencia Pride, Lemon Zest, Sweet Tart and several others seem to grow more vigorously here in SoCal but the droopy growth habit remains on many of these varieties.
The Florida Turpentine rootstocks can grow ok as Frank mentioned, if you take special care to ensure the pH of the soil is slightly acidic but this is hard to do in many parts of SoCal where soil pH is generally above 7. With a pH this high, many of the micronutrients are locked and require pH lowering amendments or a heavy layer of mulch which encourages microbial life. The waste, excrement, byproducts, exudates of the microbial life affect the Cation exchange capacity and Anion exchange capacity which allows the trees to uptake more nutrients from the soil.
If one were to utilize soil, water, leaf samples such as what would occur on a large scale agricultural setting, there would probably not be any issues using Florida rootstock. There are tensionometers that can be utilized to tell you when and how much to water and many other technologies that can be utilized to succeed with growing Mango here in SoCal but I’m more focused on helping the average backyard hobbyist gardener succeed with growing Mango here.
The cost and complexity in regards to the above mentioned techniques is enough to scare new would be Mango growers away from this hobby and I have been bringing up the potential issues regarding Florida rootstock trees ( when grown in SoCal) so that others can avoid all the problems that may arise from selecting the less than ideal rootstock.
So far from my observations and back yard experiments, Mango seedlings are the best way to grow Mango trees. Mango seedlings grow with vigor, are much less droopy, do not have issues with pre mature lignification of thin branches and will not be stunted from flowering because they are not grafted with mature scion wood.
Simon