Had a contractor install a composite railing on my deck and he did not use brackets to secure the railings he just screwed it to the posts. This was 3 years ago, it looked great at first but, over the past 3 summers the rail have started to sag due to high heat, the putty is coming out of the screw holes and it doesn't seem safe. He is out of business and the company that manufactured the railings indicated their warranty was voided because the contractor didn't use brackets. Help..........is their any kind of bracket that could go over the 4x4's and attach to the railings. Maybe a bracket on each side that I could bolt through? Really can't afford to remove the railings and start over.
Without seeing a picture it is hard to say.
My experience with wooden furniture is that when you put it outdoors bad things happen, especially if screws and nails are used to hold it together. It is pretty rare to see a deck older than 10 years that does not look like a potential termite habitat.
In general, putting corner braces under the railing would certainly provide a lot more support than a screw through the top. Unless you bolt the corner braces you will still have the screw deterioration problem. This can be mitigated by using brass or stainless steel screws. Bolts, of course, tend to have that Frankenstein look, but at least they hold the wood heap together.
My guess is that one to two years from now we will start getting questions about decking deterioration from you.