The Gladiator Lancer was first introduced as a deployable unit in WH40k 9th Edition, and remains available in 10th edition (the current edition). As would be expected, the in-game version of the Gladiator Lancer is also a long-range artillery piece specializing in taking down heavily armoured enemy vehicles and monsters. In both editions the Lancer Laser Destroyer has a massive range of 72", allowing it to target nearly any unit on the standard 44"x60" field of play as long as it has line of sight, and has very high Strength, Armour Penetration, and Damage characteristics while only being able to fire 2 shots per Shooting Phase. Even with its powerful stat-line, the Gladiator Lancer is point efficient to field. Standard competitive WH40K armies have a point limit of 2000, and the Gladiator Lancer costs only 120 points in 9th edition and 160 points in 10th edition.

It would be easy to assume that a Powerful, Cost Effective Unit would be make it a mainstay of competitive Space Marine army lists... but with the Gladiator Lancer that's not the case (at least in 10th edition I'm sooo not dedicated enough to go searching for 9th edition top 4 finishes). Space Marines often suffer from a glut of available unit options, and 10th edition is no exception. The Gladiator Lancer sees competition with the Ballistus Dreadnought, Vindicator Battle Tank, and even its smaller cousin the Predator Annihilator.

Both the Ballistus Dreadnought and Vindicator Battle Tank see heavy play in competitive Space Marine armies, compared to the middling play the Gladiator Lancer sees.

While the Ballistus Lascannon is weaker than the Lancer Laser Destroyed in almost every regard, its 48" is still large enough to cover a large portion of the battlefield and its statline still leaves it effective as an anti-armour artillery piece. What really makes the Ballistus Dreadnaught a more powerfull piece is it also has long range anti-infantry capabilities with its Ballistus Missile Launcher, which can fire frag missiles to take out globs of enemy infantry. The Ballistus Dreadnaught also has its reasonably strong Armoured Feet as a melee weapon for any melee infantry that manage to close the distance to it. At 150 points, the Ballistus Dreadnaught is weaker as a dedicated anti-armour artillery piece but its versatility makes it edge out the Gladiator Lancer.

The Vindicator Battle Tank, strictly speaking, does not fulfill the same role as long range artillery due to it only having a 24" range on its Demolisher Cannon. That being said, the similarities of the Demolisher Cannon to the Lancer Laser Destroyer I think are hard to overlook when talking about the glut of similar units in Space Marine armies and how they play into competitive choices. The Demolisher Cannon has only one less Armour Penetration than the Lancer Laser Destroyer and has the same strength. It does a pretty significant amount less damage, dealing only 1d6 damage vs the Laser Destroyer's 1d6 + 3, but the Demolisher Cannon makes up for this by having a massive 1d6 + 3 attacks which gives it devastating damage potential against not only vehicles, monsters, and standard infantry but also against heavily armoured elite infantry.

Both the Ballistus Dreadnought and Vindicator Battle tank see much more play in competitive lists than the Lancer Gladiator, with some armies even taking both Ballistus Dreadnoughts and Vindicator Battle Tanks. The Lancer's otherwise strong profile being overshadowed in such a way showcases just one example of many of the problem Space Marine armies have with being oversaturated in models, a situation born from Games Workshop constantly pushing new kits for popular army in order to sell more plastic despite potential negative affects to the game itself. Weeee capitalism.