At DLR, it is really easy to predict high crowd times (e.g. Halloween Time, Holiday Time -- especially Christmas Week, most Mondays, etc.), but it is really hard to predict low crowd times. It's not that there are never low crowd days, but they aren't consistently predictable, especially far in advance. So with that in mind...
There are pros and cons to high and low season. High season means more crowds, but more importantly, it means that the parks are prepared for those crowds. So you will get longer hours, more staffing, rides running at full capacity, fewer/no refurbs, full entertainment schedule, nightly entertainment, etc. When the parks are prepared for crowds, things run much more smoothly and you don't really feel the crowds as much. Low season does not mean low crowds! It means more refurbs, shorter hours, less staffing, rides running at lower capacity (so longer lines because there are fewer vehicles running), longer restaurant lines because there are fewer CMs working, less entertainment, nighttime entertainment on weekends only, etc. And you will feel like the parks are more crowded because there are fewer things going on to spread out the crowds and fewer CMs to deal with everything.
We tell people here to stop trying to second guess crowds and to stop betting on the crowd calendars (which are notoriously unreliable for DLR). Just pick the dates that work the best for you, then come here to double check that nothing crazy will be going on at the same time before you book. Then do your research, make your plans, have a plan A and a plan B, and get ready to let go and let the magic happen. And we'll be here to help you plan your trip all along the way!