Roberto was red hot for the first several months as RB, and then when moved to CM/RW/DM/etc. he was consistently one of our best players, ironically enough when he wasn't playing as RB. You say we have a tendency to only remember his peak performances, but I'd say you have a tendency to ignore all good performances except the dominant ones.
In Bob's 3 seasons in Ateam:
1. in the 1st season people cursed and asked why on Earth we kept this guy on our rooster at all?
2. in the 2nd season, the same. But in the 2nd half, he started to play good as a CDM at some home matches against poor teams where we were winning 6:0 with virtually any lineup (Pedro, Rafinha, Roberto, Bartra, Adriano)
3. in the 3rd season, he is hailed as a revelation, even though he played well in the 1st part of the season and returned to mediocrity in the 2nd part of the season.
So, out of 3 Seasons here, he had 3-4-5 good Months in autumn on 2015, and ironically, even then he didn't play majority of those matches as a RB but on some midfield positions when we had only Raki-Iniesta-Roberto (Arda unavailable, Rafinha seriously injured)
Now, let's look at the actual stats about Bob as a RB, and not urban myths and hype from Barcaforum.
Roberto 2015/16:
https://www.whoscored.com/Players/90782/Fixtures/Sergi-Roberto
Alves 2015/16:
https://www.whoscored.com/Players/5780/Fixtures/Dani-Alves
When Alves and Roberto are together on the field, it means that Roberto didn't play as a RB, but as a midfielder.
When Roberto is playing and Alves not, that usually meant that Roberto was a RB.
In 2016, we also have Vidal as a RB in lots of matches.
But you can also check a match centre for every match.
Roberto as a RB:
Bilbao:Barcelona 0:1 enters as a sub (Alves injured)
Barcelona:Malaga 1:0
At M:Barca 1:2
Barcelona:Valencia 1:2
Barcelona:Gijon 6:0
That's it.
Seriously, that's it (I looked only La liga matches. Maybe he played some matches as a starter in copa or in CL group stage).
Roberto was red hot for the first SEVERAL months as RB
But this is "my problem" with hype on this forum.
Just look at various topics and you'll see tons of posts with: don't worry for a RB, we have Bob. Bob is awesome. He was awesome last season. He proved that he can play awesome. Do you remember how he played at Santiago Bernabeu?
And posts like yours: he was red hot for SEVERAL Months? Ouch.
Like when? This is one of those myths created on this forum about a lot of players.
When we are talking about Bob as a RB, then, I don't get the optimism.
When you look at the stats, a guy played 4 La liga matches as a starter for Barca, and has a few minutes as a sub.
And those matches were 3 home matches at Camp Nou against Malaga, Valencia and Gijon.
And one tough match, against AM at Calderon.
So, for a RB position we have:
1. Vidal, for whom a majority of forum say that he is bad and not good for us
2. and Roberto, who played 4 and a half matches as a RB in La liga in his whole career
He was good in 2 matches and meh in other 2 matches.
So sorry if I don't share the optimism about some things like majority of guys here. (I won't even enter into a discussion of our midfield "quality" for the biggest matches outside Iniesta and Rakitic)