Rubbish. You can make hop additions to kits without making them overly bitter. Just because it's a hop addition doesn't mean it has to be boiled for an hour or whatever and give a shitload of bitterness. 20-30g boiled for 5 minutes in some of the unhopped extract and water will give a bit more hop flavour. Making a hop tea by steeping hops in just boiled water off the heat for 20 mins or so will provide some flavour and aroma. Lastly you can throw hops into the fermenter as a dry hop to get more hop aroma. Not saying the OP needs to get into this straight away, but adding hops to kits doesn't make them overly bitter if done properly and in line with the style and it does improve the basic kits.
If the tin label has an actual beer style on it e.g. Traditional Draught, Old Dark Ale or something, then it's a pre-hopped kit. If it simply says malt extract then it isn't. Also, the kits are usually 1.7kg, the un-hopped extract tins usually 1.5kg, so that's another point of difference.