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Sorry but your brother is talking rubbish and also not backing up his opinions with anything specific.
Car manufacturers will revise some details as production continues and some of those revisions are good and some not so good, depending on what you prefer. Example - VW changed the glass tint from blue to green - I much prefer the blue, someone else will prefer the green.
Much as we may criticise and find fault, the German manufacturers offer very well built cars which tend to last.
It's considered wise not to buy any car in its very first year of production - Not because it's rubbish but because the next revisions might iron out initial issues if there are any.
Some will prefer the Mk4 and others prefer the Mk5 - All for a great variety of reasons, but the 2.0T FSI engine is award-winning, literally!
[I have an 05 plate Mk5 GTI with 58,000 miles and sweet as a nut]