Remember the tilemap support in its current incarnation is very much a first release. We're aware it's missing many features and we plan to keep adding features over the next few updates. This is part of our release early, release often strategy - it's already been useful to read all the feedback about it and see where we want to take things in future.
We don't want to reinvent the wheel, but we also want to make everyday tasks simple and easy in C2. Things like supporting collision masks is not reinventing the wheel, just something we need to add support for. On the other hand we want to try to avoid reinventing the wheel inside of Construct 2 as well - given we have things like Sprites which can be animated and have collision polygons, it's worth taking some time to plan how it's best to approach some of these features. Maybe it's worth adding that functionality again but separately for tilemaps, or maybe it's better to try and get the existing Sprites to do the heavy lifting. I suspect it'll end up being the former, but working out how to add tilemap editing to an existing and well-featured editor is something that should be approached thoughtfully. Hopefully the next few releases will address most of the immediate concerns about tilemap support.