You can be a fantastic player using just a mouse. In my personal opinion it's harder to use a mouse than a tablet, but I'm also heavily biased (having used a tablet for years and also being left-handed with a right-handed mouse).
Even being the case that I'm left-handed, I still made it up to 4* maps with a mouse before switching, and that's a major handicap. I eventually switched because I couldn't do spinners (of all the things to be bad at...)
If you're more comfortable with a mouse, or if you don't have money for a tablet, keep using a mouse. If you ever want to switch, there will be a certain period where you'll have to get used to a tablet, but the reading skill and tapping ability will still be there, so you'll catch up much faster than you would otherwise.