Balde is overrated. Already made a claim elsewhere that there are at least 3 Spanish players that are better players: Cucu, Grimaldo, Cardona. Fancy that Spanish Benfica left back as well, forgot his name. And there are many others non-spanish options.
That being said, I agree, money should be spent elsewhere. Like new striker, gk or a left winger.
As long as Balde's development hasn't ended, I would still place my bets on him to become a starter for a decade. He made three steps forward in his first season under Flick and let's see how he does in his second.
Grimaldo will soon start to decline, as full-backs tend to decline before other positions together with wingers, due to their nature of being an explosive fast-pace player.
Also having played 7 years in the Portuguese league isn't the best performance proof either.
And I don't know about Cucu. His market-value on Transfermarkt is 30m, the half of Balde, while being in his prime. He gained much prominence in the Euros and because for Chelsea money is worthless.
I don't see them better than Balde, especially because Balde has by far the most potential in him as a 21 year old against near 30y and 27y.
It's going very good with Balde as starter, so if the club wants to change that position for a high fee, the new player needs to be 1-2 lvl above Balde and I don't know many who are right now.