I think you need to justify what you mean by ''huge variation'' and ''changed an awful lot''. To give you a steer, are the differences doctrinal?, do they differ on the important facts?
Well there are people who spend their time working out the number of variants between early versions of the gospels - and the typical view is that there are more variations than there are words in the bible - so an awful lot.
Now of course most of those are errors or minor variants that have no doctrinal relevance.
However not all are:
So here are some examples of changes that appear in later versions (from 400 onwards) that don't exist in the earlier version we have (from about 200-300 onward and are likely to have been deliberate additions:
John 5: 7-8 Doctrine of the trinity
John 1:18 - Jesus as unique god
Luke 22: 19-20 - doctrine of atonement
John - adulterous woman
Mark 16: 9-20
None of these appear in the earliest version but are included in later versions and from about 400 onwards are established as part of the gospels although they weren't included perhaps 100 years earlier.
We only know about those changes as by good fortune we have before:after versions so we can see that they start to appear. Of course we have no versions within the first 150 year-ish from original writing, so we have no idea what equivalent additions were made, or sections removed. We simply cannot say and we certainly cannot assume that the earliest extant version we have are the same as the original.