Masonry bits dulling after 3-4 holes
The hammering action of the drill isn't activating


So the bit is overheating due to friction. It is supposed to hammer the material you're drilling into dust then evacuate it, not rub it off through friction.

You have to activate the hammer action.

Pretty much the only use cases for not using the hammer action are when drilling into ceramic tile to avoid breaking it, or drilling into plasterboard or other soft materials where hammering will smash through and make a crater on the other side...


  Is this a better job for an impact drill?


Advantages of cordless hammer drill's are 


Light weight.
Convenience, you can drill the hole and drive the screw with the same tool.
It works for a few small holes (like less than 6mm diameter) in easy to drill materials like brick, cinderblock, soft stone (limestone), etc. 


Drawbacks: noisy and underpowered, slow/useless on tough materials (hard stone, concrete especially if it contains rebar).

If you want to make lots of holes, or diameters like 10mm and up, or drill into tough stuff, a rotary hammer with SDS+ bits will be a LOT faster. 

Don't get an impact driver for drilling, impact drivers are for bolts and tough screws, not for drilling.


  I don't have a means to sharpen it, but just from visual inspection it looks OK


It's tungsten carbide, you can't really sharpen it. Besides, it doesn't need to be really sharp, it's basically a tiny hammer with a blunt point.