If its for your own purposes, do it, use the premade art.
Ready made art is frowned upon yes, but depending on the art pack people can't tell they're ready made. I buy art packs and make games with them to improve my engines without wasting time on art. If the games have an undesirable style, no one would play it to test it. In small game jams I see art packs in the winning games and they're praised for their art by people that have no idea they used an art pack. It feels like an unfair advantage especially if no credit is given (and if credit is given who looks at the credits anyway).
I've been at pixel art for 15 months. People tell me I'm good, but I'm not as good as I want to be. If you want to get good at art or anything for that matter, force yourself to do it 2 hours a day. Block everything else out and just art. I've also discovered that great colors can make up for lack of detail or talent.
A few people have told me over the past year my games would look like they're worth more money and sell more copies if I went to digital painting rather than pixel art.