You are correct in that past updates of the game gardening, baking and certain hobbies were much more efficient in payout rate than careers. However, with the most current update (version 5.12.0) after all of the milestone quests and challenges, careers finally make as much, if not more, money. Here are the numbers to back this up.
Here are the rates for gardening and baking, sorted by highest to lowest rate per minute. This is assuming you purchase seeds and ingredients at the grocery store to procure the lowest price.
Gardening
Bell Pepper: §8.00 / minute
Carrots: §5.80 / minute
Corn: §4.50 / minute
Watermelons: §2.53 / minute
Potato: §2.17 / minute
Zucchini: §1.75 / minute
Onions: §1.61 / minute
Beans: §1.36 / minute
Hamburger: §0.63 / minute
Garlic: §0.36 / minute
Pumpkin: §0.35 / minute
Chilli Pepper: §0.18 / minute
Baking
Hot Cross Buns: §1.50 / minute
Cookies: §1.00 / minute
Heart-Shaped Chocolates: §0.75 / minute
Pancakes: §0.60 / minute
Apple Pie: §0.45 / minute
Muffins: §0.43 / minute
Choc Pudding: §0.25 / minute
Cheesecake: §0.17 / minute
Gingerbread Sims: §0.14 / minute
Caramel Slice: §0.12 / minute
Croissants: §0.10 / minute
Danish: §0.10 / minute
Turkey: §0.08 / minute
Pumpkin Pie: §0.03 / minute
This doesn't include transgenic crops or bakery items, which have a failure rate of somewhere around 50%, so in the long run those don't necessarily pay off. The quickest crops and baked goods in general have the best rate.
At the highest level (5), here are the equivalent rates for working at a career, sorted by highest to lowest pay rate.
Careers
Actor: (5 hours) §6.20 / minute
Real Estate Agent: (5 hours) §5.08 / minute
Athlete: (6 hours) §5.00 / minute
Musician: (7 hours) §4.17 / minute
Teacher: (5 hours) §3.48 / minute
Politician: (6 hours) §3.39 / minute
Artist: (7 hours) §3.00 / minute
Scientist: (8 hours) §3.00 / minute
Fire Fighter: (9 hours) §2.78 / minute
The added benefit to having a career comes when there are particular goals that are career related (such as, send 5 Sims to work, or start a career as a politician) or in order to fulfill life-dreams for orbs. In the case of orbs, career life-dreams are much more efficient than many of the other life-dreams, and still enable your Sim to have time to partake in other hobbies and/or gardening or baking when they're not at work.
As you can see, the careers aren’t necessarily much more time-efficient than gardening, however, unless you want to spend 30-second intervals gardening, you are better off having your sims go to a career. They will also make more money at a career while you’re sleeping than doing a several hour gardening task.
All of this information is subject to change with future game updates.