Learn Swedish: Strategin är ganska smart. - The strategy is quite smart.

No. Degree adverbs like ganska (quite) don't affect the adjective's ending. The adjective smart still only needs to match the noun it describes. Since strategin is an en-word in the singular, we use the basic form smart.

How strong is ganska compared to väldigt?

Ganska means "quite", "fairly", or "rather". It actually softens the adjective, making the statement slightly weaker than if you just said Strategin är smart. If you wanted to emphasize how incredibly clever it is, you would use väldigt (very) instead.

Why is "the strategy" written as strategin and not strategien?

The base word is strategi, which is an en-word. Because it already ends in a vowel, Swedish simply adds an -n to make it definite ("the"), rather than the usual -en. This makes it flow better and avoids an awkward double-vowel sound.

Is smart a loanword, and does it follow normal Swedish grammar rules?