Custom road bike build - cheaper than prebuilt?

So I got bored and decided to check some road bicycles. [color=#000000]Sarkari Result[/color] [color=#000000]Pnr Status[/color] [color=#000000]Showbox[/color]


So after looking I decided to check parts by parts, getting the best value/money of each part currently on the market of what I wanted; it's all pick and match and the resulting bike looks weird af; but overall having an ultegraish level, but at 7kg w pedals!... for around 2100 euro.

Is it possible or there's something I am forgetting?... I just don't get it; are the weights skewed down of single parts?... My math doesn't compile. I built my XC bicycle the same way and the bike ended up heavier, bolts + sealant + axles seemed to add on; is there a way to fully corroborate weights, because otherwise it sounds like a good deal.