If you keep them until their wheels fall off, you're going to need some advanced mechanical skills, I think. Everything is complicated.
I make more profit doing tree work than my retired neighbor-mechanic charges, and he's outfitted, and better at mechanic'ing, welding, working on old machines.
Maybe you need a good mechanic and a tough work truck????
You can make a good chunk of money on the side by being a good spurless pruner, creating small amounts of debris, either for homeowners to handle or to haul in a trailer, and removals where you Put On Ground Only, or buck the bigger wood.
House clearance (house sales need someone to come in NOW, for a little job)...need Lic, Ins, bonding to work for Realtors/ get their recommendation to their clients.
View screening and view improvement pruning.
Fixing ornamentals that their landscraper has screwed up.
You are competing with equiped and non-equiped companies/ people. If you are good enough at spurless pruning one important tree, you might get a couple little cake-walk removals, too, that would have gone to the other guy.
If you went to the doctor and understood everything they said, would you be a bit worried? Proper terminology to back up knowledge and experience can sell the pruning job---
3-step Targeted Branch-collar pruning cut
Branch protection zone
CODIT
Compartmentalization ("quarantine", "seal" not "heal")
Seasonal timing (disease vectors, trees that 'bleed' a lot, not when "going to sleep or waking up".
Removals need the large amount of material processed effectively to make money.
Would you rather be paid for moving 200 pounds of climber around a tree where they can't get a bucket truck, pulling a trigger or handsaw, and not smashing stuff, or being a material handler, raker, blower, truck driver, disposal operation?
A local arborist, who had some injuries, has a 6" vermeer and a Tundra, only does ground-based pruning. Low overhead. One mouth to feed. Totally on his schedule.
When its sh*tty weather, don't worry about making a payment, stay inside with the family.