So, what is the Rock-type?
Most RPGs have some sort of rock monster, generally a rock golem. The most famous of these would be the Rock Golem of Final Fantasy, but in its initial game, Rock Golem was actually weak to physical attacks. Only after the second game did Rock Golem became a defensive beast with one crippling elemental weakness, which became the basis of other Rock-based enemies from other series.
In its initial design, Rock-type was meant to be the primary physically defensive type in the game, but after the introduction of Steel and power creep in general Rock has shifted to a more offensive role. Rock's lack of accuracy and moves hinders the type from developing further however, and the ever-present nature of some of the previous generation early rocks stifles the potential competition.
The History of the Rock-type:
In its initial introduction Rock-type was an underutilized but pivotal type. Though Rock-type was destined to somewhat suck due to its status as the first boss type player encounters in the game, Rock-type still successfully kept its status as a defensive and offensive type. This was partially due to overpresence of Zapdos in the competitive metagame, and the rest of the Flying Legendaries. Sadly, only two moves were present, Rock Slide and Rock Throw.
Another historic association of Rock-type was between Fighting and Ground-types. Ground/Rock was the primary type combination for the Rock-type throughout two generations, and many Fighting-types gained access to Rock Slide, the only Rock-type TM in the game. In addition, many fossil types had Rock-type as their primary type, and this idea is preserved for the rest of the series.
Second generation was largely a joke for Rock-types. Only two major Rock-types existed, Sudowoodo, which is joke Pokémon, and Tyranitar, which was a post-game pseudo. One of the Rock-types in the previous generation, Onix, has shifted to Steel-type even. There was also Corsola, but nobody cares about Corsola. However, Rock-type still gained two weak but common moves, Ancient Power and Rollout, and its own weather, Sandstorm. The latter would be much more significant later on.
Third generation was another joke round for Rock-types. With the exception of relatively unique fossils, all the type representatives introduced in this generation were hilariously bad. The new moves introduced in this generation, Rock Tomb and Rock Blast, were terrible in their first incarnations. The new abilities introduced were also largely terrible, besides Sand Stream. At least the type got a Legendary though.
Fourth generation was a false start for Rock-types. Special-Physical split did not effect Rock-types much, as they were already heavily Physical, but now the Specially oriented types they were weak against had strong Physical moves as well, making their lives even more miserable. Rock-type was at least given some compensations, though, such as the Sp. Def boost from Sandstorm, tons of powerful moves like Power Gem, Stone Edge, Head Smash, and the metagame defining Stealth Rock, as well as the ever-popular Rock Polish. This did not help Rock-type much, but it showed the world it can be useful, and useful it did.
Fifth generation was a low level renaissance for Rock-types. With powerful species like Terrakion, Archeops, Crustle, and the benefits of permaweather, Rock-types became a true threat. While they still lagged behind other Earth types they enjoyed great use. Newly buffed abilities like Sturdy, Storm Drain, and new abilities like Weak Armor gave Rock-types a lot to play with. Rock-types also finally got a properly accurate move, Smack Down.
Sixth generation was where everything went downhill. Permaweather was over, Gems were gone, Fairies were on the rise, and many Water and Grass-types came back for revenge with their Megas. The only thing Rock-types got out of this deal was Mega Diancie, an arguably broken powerhouse that can dent holes like it is nothing. Anything else was either cool but inefficient like Tyrantrum and Barbaracle, or weaker than they should be like Mega Tyranitar and Aerodactyl. Even Aggron ditched its Rock-type for its Mega evolution.
Seventh generation was where Rock-type tried to patch things up in-game. Three famous Rock-types were introduced in this generation and marketed heavily, Lycanroc, Minior, and Nihilego. In addition to this was Alolan Golem. There were some minor buffs to Rock-type species and moves as well, but it wasn't anything substantial. Rock-types finally got an Elite Four in the form of Olivia, however.
The Overview of Rock-types:
Rock-type is a fragile offensive type stuck as a defensive type. That's basically it. That's all there is to the Rock-type. Rock-type simply has far too many weaknesses to be sufficient as a defensive type, but because it has a large offensive capability, it clearly fits better for that role. There are some Rock combinations that actually can work as relatively defensive, but they need Sandstorm support.
Rock-type however has some baggage. One major baggage is the perennial fossil Pokémon, which are always Rock-type. The second baggage would be Rock-type's role as an early wall, which always curbstomps the players, especially since the Hiker class exists in every game. This allows Rock-type to keep some continuity, even though that continuity isn't exactly great.
Rock-type is not something to be redeemed. It is meant for early game and in-game, and its role in competitive is largely in the sidelines. Even with a new type's introduction, there isn't much to do for Rock-type. It serves its purpose well enough to be not become terrible, but it is specifically designed to be terrible regardless. (I still like it though).