Is inbreeding really efficient at producing homozygosity?
And the same is repeated , production of F2 offsprings with 50% possibility of heterozygous individuals.


That's not correct.

Let's start with a population with 100% of heterozygotes:

100% Aa


And, just to create a highly exaggerated model, let's suppose that these individuals perform the most drastic case of inbreeding: self-fertilization. Inbreed occurs when an individual perform sexual reproduction with a closely related organism, and no one is more closely related to someone than himself!

After the first "inbreeding" generation, we'll have:

25% AA
50% Aa
25% aa


So, 50% of heterozygotes.

If this population inbreeds again, we'll have at the second generation:

37.5% AA
25% Aa
37.5% aa


So, 75% of homozygotes versus 25% of heterozygotes.

In the third generation:

43.75% AA
12.5% Aa
43.5% aa


And in the fourth generation:

46.875% AA
6.25% Aa
46.875% aa


Thus, in only 4 generations, we have 93.75% of homozygotes versus 6.25% of heterozygotes. Mathematically, the heterozygotes never disappear. Biologically, however, if a population shows self-fertilization, heterozygotes disappear in few generations.

Now, let's get out of this overly exaggerated example with self-fertilization and back to your question, where the organisms perform cross-fertilization:

The problem with your reasoning is that (correct me if I'm wrong) you're starting with a couple (Aa) and supposing that all their descendants will mate randomly. Of course, the allele frequencies will remain the same. But that's not inbreeding. By definition, inbreed is a non-random mating system. For a real inbreed to occur, the mating individuals should be more closely related than
those drawn by chance from the population.

In conclusion, given enough time, inbreeding (and genetic drift as well) has the effect of eradicating heterozygotes from the population.