Was always a relatively limited player offensively in terms of playmaking abilities and technique (say compared to a contemporary like Marcelo who is a few levels above him in that department), overall, but the few obvious strengths of his (pace, stamina, making runs, providing assists and his cooperation with Messi) made up for it.
However he has always been suspect defensively and prone to brain farts and losing focus.
Having said that he is no doubt among the elite LB in the past 10 years. However nowhere close to say Alves and I would rank Marcelo a level above him or two even.
I would want to see Malmierda give Firpo frequent playing time from this season onwards already. Alba should only be playing 60% of the games. Can't have him think that he is untouchable when he will turn 31 years in a few months time and survives (on this level) mostly due to his pace which he is likely to lose in the next 1-2 seasons.