I don't know if it is a dialect thing (I'm from Stockholm), but I would say that 'jätte' is a familiary/spoken language thing, to intensify, used instead of 'mycket' (very). It's so common that it isn't such a big deal anymore. But of course 'riktigt stor' is another way of saying 'mycket stor' (very big), and people who take care of their written language will not use an illogical expression as 'jätteliten'. And in that case probably avoid it also when talking.
The thing is that 'veramente', 'molto', 'davvero' is all adverbs, right? But 'jätte' is really a noun in Swedish, a fairy-tale figure, like "the green giant" = den gröne jätten. But 'jätte' is also used as a measurement, meaning 'really big' (like a giant), but has evolved even further, to mean just 'very very', and can therefore be combined with 'small'; jätteliten = very small