Nice input and welcome to NB
You're not seeing what I'm trying to say
Like I said, Ichigo has the reiatsu to overwhelm most people in Bleach, but he doesn't have the type of training that the Gotei 13 have
To compare in practical terms, Ichigo is like a street-type fighter. He's nearly self-taught and quite good might I add. But he lacks the techniques, precision, and efficiency that the elites of Soul Society have. The Gotei 13 Captains are like professionally trained and polished fighters
Ichigo had to go balls out against Grimmjow. He needed his Mask, Bankai and Inoue's damn tears to defeat him. But when Kenpachi came he easily finished his battles after he stopped goofing around. Ichigo even defeated Kenpachi in their first bout. This in itself shows that Captains are still getting stronger and are a step ahead of Ichigo. As far as the Gotei 13 is concerned, even if Ichigo is powerful he is still a growing rookie
If Ichigo were to go up against Byakuya he could likely tie or even lose. It's not
all about brute reiatsu. It's not like DBZ where their Power Level (seriously, a single dumb number) defines their
entire fighting potential. In Bleach, there are other things that factor into who can beat who
Examples:
-Ichigo has no knowledge of Kido, let alone be able to counter Kido. Had Ichigo gone up against Zommari instead of Byakuya he would have surely lost
-Ichigo has little experience/training in hand-to-hand combat and close-quarter techniques. If he goes up against Yoruichi or even Soi Fong he would lose
Just because Ichigo has a lot of reiatsu (nearly twice more than an average Captain according to Unohana) doesn't automatically mean he can beat everyone else. Sheer reiatsu doesn't define overall prowess and/or strength. It's about being able to harness your reiatsu effectively and incorporate them into your attacks and fighting techniques
Again, like I said initially, this is assuming Ichigo doesn't still have his pre-FGT form, which was stupidly ridiculous to be honest
