There's an easy way to check for correctly matched levers and brakes. With a correct match, the shoes will close about 1/8"max per side or 1/4" total before the lever touches the bar
It's simple leverage, travel vs, force. So if your brake shoes open 1/8" or more per side your levers do in fact lack leverage. OTOH, if the brakes are nicely adjusted and close 1/16" per side or less in half the lever's travel, you won't be able to use more leverage, and need to look elsewhere for your problem.
Note, that replacing cantis or V-brakes on a mtn frame involves large calipers. Even if the leverage is correct, there'll be a decent amount of flex in the arms and braking will be poor. That's why only bottom end 26" mtn bikes come with caliper brakes in the first place. The Canti's or V-brakes are inherently more expensive to the manufacturer, involving mounting the bosses on the fork. They weren't used for style, but because of performance.
If you have canti bosses on the fork, consider going back to canti or V-brakes.
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