yes, there are features that are strangely omitted from the Commsec implementation of Viewpoint - market order is one of them and I think you're correct that it may be an intentional decision.
I'm not impressed with having to use the app or the website to execute such a basic order, it's meant to be a premium platform from a premium broker.
I've done the free trial of Spark a few times, it's actually $250 per month with the base fee
plus at least one data pack - that's getting a bit expensive for how often I trade.