I agree.
If Barca wants Dembele and the club is finally able to get him, let it be. But shouldn't forget that his final 120-150M price is just and simply because of the Neymar deal.
His "2017 June value" would be around 40M.
My concern is a bit more on his professional or his accomplished qualities though. He is a young, fast, good player, playing in a team that is almost built around counter-attacks. His good speed was a nice thing there, but Barca's style is very different. He is still not a Neymar type of player (not as skillful and even not as fast). Thus, though I'd wish him the possible greatest success in Barca, if he comes, frankly and professionally speaking, I don't see the concept in signing a Dembele type of player, unless there were quite a few other changes as well, and a handful of changes in Barca's style.
If he is brought to complement Neymar's departure, then he is a bad choice in my opinion.
Unless Coutinho comes and by that there is a chance to overhaul the midfield this season, Dembele alone will not be a wonder-maker and even with him there are hordes of other factors to turn to Barca's advantage to play on the level of the 2014/2015 season.
Expectation will be extremely high for a player of 150 million, and I'm afraid Dembele is not surely the type of player Barca really needs.
Regardless his present state, Di Maria is much closer to the type of player this system requires to continue.
But this is just my personal opinion...