For some reason, quite a lot of Gen V Pokémon struggle with bad movepools. Klinklang is another offender; it's a physical-based Pokémon whose only non-Normal physical moves are Gear Grind, Rock Smash and Wild Charge. In BW it didn't even have the latter, and as Rock Smash is no longer a TM that move has fallen out of its current-gen movepool too. Klinklang is a Pokémon that reaches its final form at level 49, but it doesn't learn any usable STAB moves after level 16.
And that's the thing that leads me into the thing that annoys me in this post: Gen V has been kind of neglected since it came out. BW and BW2 were neat games, and the Unova dex is one of the best standalone rosters Pokémon has ever seen, but they never got the kind of attention other generations got in their preceding generations. Neither Megas in Gen VI (except Audino, probably the Mega Evolution fewest fans wanted) nor regional forms in Gen VII. Movepools are mostly unchanged for most of them, even the starters' movepools are nearly identical in Gen VII to what they were in Gen V. It's neat that Heatmor, of all Pokémon, got a signature move, but it was far from the only Gen V 'mon that needed a buff.
Part of what makes Pokémon so great to follow over time is the various changes and buffs older Pokémon get in new games. Jokémon such as Sneasel, Politoed or Mawile have received upgrades that really allowed them to shine, totally changing how they work in battle and how they are viewed by fans. Gen V came after many of these upgrades, such as cross-gen evolutions, the rapid expansion of available moves or the addition of another ability slot, so naturally its Pokémon haven't had the same opportunity for growth as, say, the Gen II Pokémon. But the last two generations have come with many such upgrades as well, i.e. Mega Evolution, regional forms, stat tweaks, signature Z-moves, and general movepool expansion, and Gen V hasn't got to take part in very much of it. Game Freak pushes more upgrades for earlier generations, but post Gen IV it appears that generations are created "readily upgraded", and continue to be seen as such even as several generations pass and the ever-upgraded early-gen Pokémon keep getting new revisions.
To be fair, it does make sense that earlier gen pokemon get more attention than gen 5 pokemon, simply because the old pokemon.... are older. Many older pokemon need buffs to make up for the increasing powercreep, while many gen 5 pokemon
are the powercreep. As you said, gen 5 has one of the best standalone rosters in the franchise. Almost every single pokemon is perfectly usable in-game already, which is a sign to me that most gen 5 pokemon are already well-designed for what they are.
The movepool issue in particular is not as big as it seems, in my opinion anyway. There are of course a handful of examples of pokemon with bad movepools, such as the aforementioned Klingklang. From the top of my head, Purrloin, Petilil and Pidove can be added to the list as well. But other than those few examples, gen 5 mons' movepools are actually very decent. Sawsbuck, Cinccino, the monkeys, like all of the dragon types, and many more. I don't think gen 5 has more pokemon with bad movepools than any other gen if you really bothered to check.
I also actually prefer movepools to be a bit restricted in general. I'd rather have sensible, specific movepools than everything getting the same common moves, just like Hyper Cutter described. Looking at a clear example, such as earthquake, the point becomes clear. In gen 5, earthquake is mostly just distributed to ground and rock types, which makes sense. The exceptions that also learn earthquake, are very powerful, bulky looking pokemon like Emboar, Conckeldurr or Darmanitan, which also makes sense. Meanhile in the earlier gens, pokemon like Chansey, Girafarig and Seviper can learn earthquake.
So basically, my point is that I don't want the gen 5 pokemon to be buffed by just overloading them with moves. I just want the pokemon that actually do have movepool issues to get fixed, but not all of the other pokemon that are fine already. I wouldn't be opposed to some stat buffs here and there though.
I think the
actual reason gen 5
seems to be ignored is because they all evolve so late, so they are not distributed in the newer games as commonly as the older pokemon. Gen 6 has this problem as well, and it shows considering Alola had very few pokemon from gen 5 or 6. If Gamefreak really wanted us to care about gen 5 and 6, they should just make gen 5 and 6 mons available in the main storyline, preferably in the early-mid game. But if they want to do that, they first have to lower evolution levels.
I'd disagree on wanting gen 5 to be a bigger part in the selection of mega's and signiture Z-moves too, simply because I don't really like mega's and I just hate Z moves. Regional forms is not the greatest argument for claiming gen 5 is ignored because you could make the same argument for any other gen except gen 1. That said, I would like to see some gen 5 regionals if they return for the Galar region. Galar Lilipup seems to be a popular one that fans want.