You forget Arthur is on his way.
Arthur will come in January of 2019 and hasn't played a minute of football in Europe.
Unless he is the next Xavi (which 99% isn't), even if he will have an impact in our team, it will probably be around 2020 at earliest.
Gomes played 2 years in La liga and looked good=when he came to Barca, 90% of people say that he is a disaster
Denis played 2 years in La Liga and looked good=when he came here, he is even worse than Gomes
Semedo was a beast in Portugal=in Barca he is unable to make 3 decent attacking actions over 20 games
Mina never played in Europe=he probably won't get too many minutes this season either
Paco played in La Liga and was called to an NT team=in Barca he is struggling
So, when you look at our recent young players, how they looked before Barca and at Barca, or how much time they needed to adapt (do I need to mention Dembele?) and how many chances EV is giving to them, I guess that it is fair to assume what I have written above: even if Arthur is a real deal, it will take at least 2 years until he will a significant impact and a number of minutes.
And if he is the same type of a deal as our recent signings, then you know the answer, he won't be any threat to anyone.
So, all in all, Arthur (or Alena) won't be a threat to Gomes in 2018/19 season.
Maybe someone could start to be a threat in 2019/2020 season.
No matter how bad you guys think that Gomes is, already under 2 different coaches he was higher in a pecking order than:
1. Arda
2. Denis
3. Rafinha
4. Samper
99% of users of this forum haven't watched a single minute of Arthur actually playing.
But a lot of guys already think that he is a real deal or that we should now sell Gomes, Rakitic, Gomes, Rafinha, Denis in order to play him and Alena.
Slow down...
Let's see how he will actually perform on a pitch.
Even way better players tuned into donkeys when they actually started to play for us.