If Dr. Strange was a cat I think the universe would be in for a big load of trouble. Not only would saving the universe be on the ‘cat’s time’, but pretty much anyone that didn’t feed the cat or scratch his belly or do whatever he wanted might be in a spot of danger if the cat so wished it. Ever notice how cats seem to almost always want their way and then disregard whatever anyone else wants? With a dog you have the idea that they’ll be grateful a lot of times and act like your best friend, but with cats it seems to be on average that they’ll do what they want and never bother to think about what might happen.
That’s why Dr. Strange as a cat kind of doesn’t seem optimal since the defense of the earthen realm from magical attacks isn’t bound to wait until Dr. Strange gets a belly rub or a scratch behind the ears that he so badly wants. That is being very general about felines but it’s also from experience and from the media bits that show a lot of cats being entirely aloof and only concerned with what they want. There are a lot of feline companions that are somehow more attuned to their family’s needs and will be accommodating so long as they get their way from time to time. Cats are usually very proud creatures and don’t tend to lower their standards like dogs would it seems. I’ve also heard many times that cats are just crazy since they do have a much more developed personality, and I wouldn’t really dispute that.
If the Sorcerer Supreme was ever replaced by a cat however I think that would make for one interesting comic book, but not so much anything else. It would have made a great What The? comic if nothing else. Dr. Strange has a certain reputation among the comics that he’s gaining quickly in the movies as one of the most powerful people in the MCU, and while it’s not because of his physical strength or prowess, it is because he can control powers that many of the other heroes and villains don’t understand and can’t easily defend against. He’s not the most powerful individual, there are plenty above him and he’s lost his fair share of battles as well. But it typically takes a heavy hitter to take Strange out, such as World War Hulk when he broke Strange’s hands. I do think that Ghost Rider could take him out as well if it really came down to it. Apart from that most melee combatants couldn’t even come close to him if Strange was fully aware of them and had a moment to fashion a spell that could contain them.
As a cat though do you think he’d bother? If someone annoys a feline they typically have at least a few moments to worry, unless the cat is already good and riled. Then, if the kitty still has claws, they’ll usually proceed to rip the offender a new one. Think about a cat that can use magic now. Anyone messing with this cat might find themselves lost in oblivion just for walking by them without scratching his ears.