The 5e Bard is a more powerful character than the 3.5e Bard, but not nearly as good at buffing his allies.
To start with, the 5e Bard gets full spellcasting all the way up to 9th level spells, where the 3.5e Bard got 2/3 spellcasting, topping out at 6th level spells. This is, in some ways, the biggest change, and it has a huge impact on the Bard's power and flexibility. Their spell list doesn't have the raw power or versatility of the Wizard, but it's pretty solid. And, of course, they get to add stuff to it. More on that later.
The next thing they get depends on your choice of College. Valour Bards get Extra Attack, and a bunch of proficiencies, that put their fighting ability roughly on par with that of a Ranger. Lore Bards, on the other hand, get bonuses to skills that make them arguably the best skillmonkeys around. This honestly isn't a huge change; the 3.5e Bard was already a pretty reasonable fighter and a great skillmonkey.
What's really different is the Bard's specialty, inspiring allies. This has, in all honesty, gotten substantially weaker. Instead of continual effects that boost all nearby allies, the Bard now has the ability to give a single ally a one-off boost. It's slightly more flexible in that the ally can choose which roll to add it to, and the Colleges add even more uses, but it still amounts to far less of a boost. What's even worse is that, for the most part, the Bard can no longer affect themselves with their inspirations.
Spells can help alleviate this, but buffing spells have also gone under the hammer. For the most part, because of concentration, you can only have a single buff spell active at a time. And, just like your inspiration, most of the good buff spells have been changed to only affect a single target.
What these changes amount to is a character who no longer sits at the back buffing, not just because they have other options, but also because they can't. The dedicated buffer is no longer a valid playstyle. You can give an ally inspiration every turn, but that still leaves your actions free. You can use your first turn to cast a buff, but you won't be able to do that on later turns.
Luckily, there's some good news coming. The 5e Bard has a unique and extremely powerful feature that I haven't talked about yet. Magical Secrets allows a Bard to select a few key spells from any spell list. This ability is incredibly important, because those spells (especially the first 2 you get) can shape your character's playstyle. The most infamous example is Swift Quiver. This is a 5th-level Ranger spell, which means it's normally only accessible at level 17. However, a Bard can learn it at level 10. This allows a Valour Bard to make 4 attacks per round with a bow at level 10, long before a Fighter or a Ranger.
So, what's the takeaway? (Or, if you're that way inclined, tl;dr)
The 5e Bard is a versatile and powerful character who can excel at most things they set their hand to. With a bit of work, so was the 3.5e Bard, but relative to other classes, I think it's fair to say the Bard is more powerful in 5e than it was in 3.5e. On the other hand, the 3.5e Bard is much better at buffing his allies than the 5e Bard.
There are not any differences as written. Using the mule statistics for donkeys seems reasonable enough, given that D&D isn't really meant to finely model the abilities of real-world creatures (and they mostly have statistics at all simply for the case of fighting 'em). The Monster Manual (appendix A) says:
OTHER ANIMALS
A book of this size can’t contain statistics for every animal inhabiting your D&D campaign world. However, you can use the stat block of one animal to represent another easily enough. For example, you can use the panther statistics to represent a jaguar, the giant goat statistics to represent a buffalo, and the hawk statistics to represent a falcon.
The difference between "giant goat" and "buffalo" probably exceeds that of mule to donkey.
If this doesn't feel satisfying, though, I think it's reasonable to work with your DM to modify to taste. As long as you're not giving it a +10 2d12 gore attack and firebreathing, I can't see why anyone would really make a fuss.
(If you do want to make your own, my offhand thoughts: Remove the Beast of Burden feature, drop its strength and raise its dexterity, and drop its attack damage too. Maybe give it more charisma, because those ears are so cute.)
Best Answer
The first map had errors. The SKT map had those errors corrected. That's all there is to it.