True, I agree. I put 18/19 only behind 10/11, 14/15 and 11/12.
Though, to be honest (and this is a dig to Valverde and the rest of that sorry team, not Messi), this "we almost got the CL/treble" claim, is a little bit misplaced:
-In La Liga we literally faced by far the worst Real Madrid team during Messi's tenure. Atletico were also nowhere near those mid 2010s teams. So, we were basically playing alone (second team finished with 76 points, a stark contrast compared to some 90+ seasons!)
-In CL we faced some rather mediocre teams on the road to the final. Lyon for the R16 was an average opponent to be fair, though it is not rare to face a much more challenging team this early on. Then 2019 ManU in the quarters was also a rather average to below average opponent for this stage. Liverpool was the first great side we faced and we choked hard. This notion that 'we would win the CL' also heavily relies on the fact that we would face the ... mighty Spurs in the final
A historically weak opponent for the final.
So yeah, great season no doubt, but maybe the main reason it is considered better than e.g. 09/10, 16/17, 12/13 etc. is this great CL run and the La Liga title, which, when put in context, are not that huge of achievements after all.