Well it is actually an explosion if all living things are supposed to be the modified descendants of one or a few original forms.
8000 known species over 30-80 million years? That's a pretty sedate explosion, don't you think?
To put gradual and sudden in context -the following analogy given by Jonathan Wells in response to criticism of his "Icons of Evolution' book - explains it well -
The problem is that Wells - who is not a biologist - explains it
wrong. You've been lied to about the Cambrian explosion, Beretta, by Wells himself and by others.
In defence of evolution, other critics of Wells have admitted that it was a sudden explosion but have argued that that is exactly what we'd expect for various other 'plausible' reasons that are actually not plausible at all.
Who says they're not plausible? You?
That was the standing explanation until soft bodied fossils were found and so it no longer makes sense as an excuse for all those missing organisms.
Soft-bodied fossils are quite rare. That we're lucky enough to have a few examples doesn't change that. Your argument is like saying that, because one guy won the lottery once, we all must have a million dollars in our wallets. It doesn't make any sense.