You're right that factory crimps can't be done with the average set of crimpers. A set of Paladin or MSD( yep the ignition folks)crimpers will set you back close to a Cnote and the jaws are about 30 bucks a set. If you properly calibrate them for a mil-spec crimp there goes another hundred. I set mine with a fish scale and I haven't had a crimp failure in years. If you inspect the ends on factory power feeds you will find they are soldered in addition to the crimp. I think you did just fine on your soldered butt joint and it will serve you well for quite some time, but when you do start having feed problems, look there first. The reason solder is used is not to transfer current from one wire to another but to hold the joint together. Solder and butt crimps don't provide this wire to wire contact and make a high resistance area in the wire that runs hot and will eventually fail.
Sounds to me like you aren't skiving enough wire on your 10ga. You need to skive about an inch and a half of wire on each side. Split each one in half for 3/4 " so you have a Y. Put the Ys together and twist the tails down the opposite wire. Use a couple pair of pliers to tighten the twist and lay down any ends. Use rosin core solder and a big enough heat source to heat the wire to solder temp very quickly so the insulation isn't effected. Use a self-sealing shrink tube to finish.
If you are t'ing off a 10ga skive about an inch and a half off the mainline but don't cut it off. Take a screwdriver and stick it through the skived area splitting the wire in half. Skive an inch and one quarter off your added wire. Stick it through the mainline split and divide it in half and wrap both ways down the mainline. Bend your added wire in the direction you want it to go, tighten, solder and finish
I'll shut up now