The problem with the Highlander/Pilot segment is the Highlander and Pilot. They're well established benchmarks that make it hard to gain traction in the market. GM has sales success and some others too, making it crowded.
BUT - yes, it's a KEY market. Production costs are not that much more than the CUV class, but higher MSRPs mean better margins. Healthy margins with good volumes mean a lot of $$ for the bottom line.
If Mazda can get a competitive product, it could make a big financial difference. But, since they lack larger engines etc, it's going to mean higher development costs. And what else can they spread those costs over? They don't have a mini-van, etc.