That's too naive. There's next to nothing known about how activity in individual neurons and their synapses relates to mental contents, in particular "higher level" concepts and thought patterns that you're concerned with in adult learning. In other words, the network dynamics are complex and unknown, and so the suppression / deactivation of certain synapses may just as well be a normal and necessary part of learning as it may be a part of forgetting, or neither. There is currently no contender for a "neuroscience standard model" that would bridge between this kind of neural dynamics and cognitive functions. I hope to live to see one.

Maximizing total synapse strength would as useful as maximizing the number of 1-bits on your hard drive. It's not what you want :)

Regardless of one’s general level of intelligence, there is that age-old adage of a trade-off between book smarts and street smarts, or any other niche skill. Forgetting, and the resulting ignorance, is part of learning. Perhaps that’s why people in modern societies feel unhappier than those in poorer, less developed societies.

Still, any society has certain forms of learning with outsized benefits that make them worthwhile.