Are there any ways normal tickets are cheaper than contactless for journeys within the contactless zone in London?
Afaict if you consider stations that are within the contactless area but outside the numbered fare zones the answer is yes.
Usually for such journeys the oyster/contactless single is roughly half the corresponding paper return. This means that for single journeys oyster/contactless is usually (but not always!) cheaper. For return journys the price will usually be around the same but there are quite a few things that can tip the balance in favour of one or the other.
Firstly railcards and child fares. Railcard discounts can be quite significant, but there is currently no way to use railcards with contactless. Some railcards can be used with oyster, but my understanding is it's a pain to get your railcard loaded, not all railcards are eligable, and not all stations that offer contactless offer oyster. There are no child fares on contactless and while child fares exist on oyster actually getting them seems to be a pain.
Secondly the peak/off-peak restrictions can be different between oyster/contactless and paper tickets.
Thirdly my understanding is that there are no "super off peak" fares on oyster/contactless.
Fourthly the nature of oyster/contactless means that the handling of multiple routes works differently. Oyster/contactless can only distinguish between two routes in specific circumstances. Either when passengers are forced through gatelines, or in some limited cases where pink readers are used.
Fifthly there seem to be some plain old anomolies. Farringdon to Gatwick on oyster/contactless is £17.50 peak by the default route. While a paper ticket routed "not underground" is only £13.10. Granted the oyster/contactless fare has underground validity, but I can't think of any sensible route from Farringdon to Gatwick that would involve the underground and wouldn't trigger one of the alternative fares.
Sixthly split ticketing with oyster/contactless requires at a minimum, existing the system and re-entering and sometimes requires additional tricks to avoid unwanted out of station interchanges.
Seventhly the oyster/contactless system can sometimes join up journeys you would rather were treated seperately. Particularly if you make a tube journey in central London towards the end of the evening peak, followed by a rail journey out of london just after the evening peak they can end up joined into a single journey and charged at the peak fare. The London terminals have very long OSI times for tube to rail interchanges (presumablly because many of them have the waiting area outside the gateline).