Dunsparce is a swarmer which complicates its acquisition. But in Dunsparce's case its status as a swarm Pokemon is especially important.
Normally we can just say: "well, we can use the DST trick to get around that so that shouldn't be a huge problem." But in this instance, it's not that simple. Part of the problem is that to do the DST trick, you first need to get the appropriate phone number. In Dunsparce's case, said phone number is found on Route 33, after Union Cave and well after Dunsparce is first acquired, so you would first need to skip past Dark Cave and progress through the game until you reached Hiker Anthony, get the phone number, and then walk all the way back to New Bark Town to do the trick. From there, you then need to go to Dark Cave to catch Dunsparce, and then you'll need to grind a level 4 Dunsparce for 10 or so levels to get it going. That's some investment!
Alternatively, you could try your luck and hope to encounter a Dunsparce without a swarm, which might pay off but is a huge gamble. Out of interest, I decided to test methods. When using the non-Swarm method, I was very fortunate and managed to find one in about 10 minutes. I was less fortunate when I failed to catch it due to a badly-timed crit, and then I spend over an hour to find the next one which I did catch. If anything, this experience demonstrated well just how risky attempting to catch Dunsparce in this way is to you time. By comparison, the more grindy swarm method took about 40 minutes from getting Anthony's phone number to having Dunsparce at a good level for battling. I consider the DST trick route to be superior just because it's more reliable and so should be taken into account when considering its availability in tiering, but that is a lot of time at that point in the game (I could very well be on the way to Ecruteak and beyond by then had I not bothered).
As far as battling performance is concerned, Dunsparce is actually decent. Early-game, it happens to benefit from its combination of high bulk and STAB Rage – it was able to beat Faulkner and Bugsy with this method and it even managed to sweep Whitney by itself (note that this isn't reliable because it depends on Dunsparce accumulating lots of Rage boosts from Clefairy's Double-Slap, but it was still amusing to observe). Later on, it can use Headbutt and Return for a more reliable option, with Dig to cover almost everything that resists it, and it happens to work ok as a route sweeper with some match-up utility, although it is a bit slow.
Ultimately though, I consider Dunsparce to be one of the worst Normal-types, possibly on par with Togepi, simply because of its availability issues: too much time and effort involved to get it, and with insufficient pay-off.