Certainly Tinkercad isn't as sophisticated as Fusion but I wouldn't say it's useless. Having designed a printed nine locos, five different designs of carriage, and around a dozen different types of wagon with Tinkercad, not to mention all sorts of other items such as points levers, name boards, fencing, signal bases, windows, gutters, level crossing gates, loco lamps and quite a few household items, I'd say it's pretty useful.
In total, to date, I've used Tinkercad to design 980 items.
I've blogged my latest 3D printed loco build which includes a section on how I used Tinkercad to design it -
How I used Tinkercad to create a locomotive - PART 2 - How I drew the various parts
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Rik