Tremor outranges Impaler thanks to the large spread it has. Barring Merlin, Tremor has the longest effective range and highest DPS of all mobile land artillery. It is effective against terraformed walls, burried buildings, static defenses, mobile armies, cloaked armies, shielded armies, it is useful as area denial, it can fire while moving. Thanks to relatively large impact radius of individual shots, effective DPS scales upwards with unit density. As far as artillery function goes, the only weakness it has is that it fires continuously and thus doesn't benefit from cloak as much as other artillery units.
All for the price of 1500. Let's compare other artillery units for the same price:
2.14 Impalers
2 Phantoms
1.78 Emissaries
1.66 Firewalker
1.5 Lance
0.93 Crab
0.42 Merlin
I'd like to point out that 2 Impalers which is the only artillery except Merlin that comes close to range of Tremor: cannot hit targets in holes, cannot hit moving units, cannot hit static units without LOS, smaller effective range than Tremor, insignificant DPS, only functions as a mex sniper
Merlin is a better Tremor in every way (except terraforming) with full benefit from cloak and better precision.
Rest of artillery has their niche filled well. Badger is a skirmisher with area denial and not artillery.