Even if you could design your own model… How do you acquire a dataset even a fraction of the size those pretrained models from corps.
Then how do you train the model in a reasonable time. Other than relying on cloud computing which leads to the same problem I outlined before of only corps can play this game properly right now.
I designed and collected/labeled the data for a relatively small deep CNN for my masters thesis and training it on 60000 images was taking over a dozen hours (this was 5 years ago at this point so that part may be misremembered) on a 1080ti.