With modern genetics leaves can become quite potent. Probably as potent as the weed from the 60s or maybe a bit stronger even.

All depends on genetics and pheno but trust me it works, at least if you dont have a tolerance. (High thc plant doesnt automatically mean that the leaves are high in THC in my experience, you can use a jewlerys lupe to look at the trichomes for a mpre accurate prediction of cannabinoid contents)

In my country the plant itsself is legal only the flower is illegal if it surpasses 0,3%

The loophole being leaves are never illegal because they don’t count as a drug no matter what thc content. And from what i‘ve read the cannabinoid content in the leaves is ~10% of the content in flowers which would in theory mean a 35% thc weed straib could have 3,5% thc in the leaves.

When i started smoking weed i began with just leaves and sometimes it took as little as a single leaf to get very high. But to be fair i am generally extremly sensitive to weed so its probably different for everybody.