Never a good idea to have connections between the motor and ESC. Worse case scenario, the contacts between the plugs isnt good, creating a point contact, which results in high resistance which may heat up the connector to the point where melted the solder and the entire connection coming loose. Even if the connection is secure enough for good electrical connection, theres still a potential that they unplug itself in a crash or whatever. Unless you cant avoid it, always direct solder.

But if you want to swap out motors easier in between classes, having a connectors would definitely help. Just make sure that theres plenty of contact between the plugs and make sure your wires arent so long that they can be easily tugged, unplugging the connection

Same thing can happen with connectors between the battery and ESC. Just keep them well maintained and it's fine.

We do this on brushed crawlers, Deans/t plug. We have burnt a motor or 2 out on the trail/rocks/mud. Always keep a spare.
How many classes are you going to run? Get a car for each class.
The bad thing about running every class is that you never turn marshal. I've seen a lot of guys do that and it's not fair for everyone else.

No to solder bullets between motor ans esc. seen many a new guys have a motor wire come unplugged.. its no real time saver even if you have 10 minutes to change motors..

learn to solder
get a solder iron with enough watts to get a good solder job
tin all solder joint before
makes the job go smooth

easy as that

learned to solder in middle school 45 years ago

Worst case scenario here is the ESC will just pop its phases when two motor leads contact each other.

Doesn't save time? I can reconnect 3 bullet plugs far quicker than I can set up and warm up my soldering iron.

Had that happen to be when the connector was too loose. Seen people melt the plastic case on their batteries too because the connector was too loose and causing it to heat up.
We should go back to the nicad or nimh days where we directly solder to the battery tabs.

Let's not do that.

Well I cut the cables for a perfectly good connection between an engine and an ESC and soldered a connector onto both. The connector can only go one way so it is impossible to attach it backwards. Also because the bullets are in a harness, it is impossible for the wires to touch each other. I used 12 AWG wire - tried 10 but was too big for the holes. 11AWG might be able to fit. I did 1 motor and 2 ESCs to test "switching" and it worked perfectly. I bought the connectors I linked up above. I have no real desire to test added resistance to the connector. The overall length of cabling went up 30-50% because I found the soldering the connector onto cables already connected to the motor/ESC more difficult to work with. When I soldered the wires to the connector first and then to the motor or ESC, it was much easier. I initially thought it was the length of the cable causing me issues, it wasn't. It was the weight of the ESC and motor. They were harder to stabilize than the connector end.

Overall quite pleased with the results. These are 1/8 scale ESC and motor so the connector might be "big" for 1/10 scale. I will be going there next.

PS - The observant will notice a 2 wire connector in the background attached to my other ESC. That is XT-90 for power, not the 3 wire for the motor.