Trying to explain it the same way I would to my 6 year old:

How the creature actually moves will have a major effect on how well it handles different gravities. Cheetahs may be the fastest land animal here on earth, but gazelle and kangaroos have better locomotion for handling lower gravity, and could potentially be faster than the cheetah, but this is because all animals would have to deal with decreased traction even in the best conditions. (Think like running on loose gravel. Where the rocks roll and kick up as you run, and you slide a bit when you stop.) This will be worse for creatures that use claws or such to increase traction at speed, and better for hoppers.

High gravity favors animals who don't hop. With thicker stubby legs. To support their heavier bodies. As gravity goes up the more land animals look like elephants and hippos. Strong stable stalks that can resist the pull.

The next major hurdle to speed is breathability of the air. At lower gravity you get less density. Which means not only is it harder for the creatures to run normally they also aren't getting the proper density of air, and will become winded needing to slow down and rest more often to catch their breath. Think how low elevation sports teams do in high elevation fields. Getting winded from their usual activities.

There are a few other things that could affect the results like if the creature is smart enough to practice different running styles, and such, but largely for most animals the experience will be too drastically different and instinct will tell them to slow down and be safe.

All that being said you can see we are asking if mini hippos would be faster if they are out of breath and running on gravel? For most creatures that will be a no, but a few exceptions exist. Just like if it could breathe the atmosphere that the mountain goat could be the fastest earth animal on the moon.