I feel like people saying MC didn't visibly grow enough are just blueballed waiting on lvl 4 and its making them miss the forest for the trees.
Part of it might also be that the MC has in fact grown so strong and has fought other strong opponents to the point where conveying the strength becomes difficult and requires a level of abstraction to appreciate. At lvl2 he was still vulnerable to large groups of humans with conventional weapons, so powerscaling MC when he beat Valravn (who mowed through humans despite them having tanks) or Jake (over a hundred soldiers iirc) was simple due to how grounded it was. Now at lvl3 you have to use a bit more imagination to understand how beefy his armor truly is to withstand blows that would've obliterated him at lvl2 or how much his brute force (not even his forte) grew to send Yuren through several floors. Moreover, the ease of transformation and the increase in his arsenal of forms isn't something you can put as concrete a number on like power level or how big a crater you can punch into a mountain, but is nonetheless a vital and significant to the growth of his trait. There's a whole lot more to his progression than "make scythe but bigger".
On the topic of Yuren, I think here is where you really see MC shine. When MC and Deryl freshly evolved, it was an even match between two lvl3s. When he fought Cole, he was outclassed in raw strength but his skill saw him through (until Cole evolved). When he fought Yuren it was so absurdly one sided it was like the MC smacking a toddler around. A fellow lvl3, yet absolutely no match for him. It wasn't quick either, so you got to appreciate the MC methodically dismantling Yuren, beating him blow for blow, foiling every single stratagem, really just flexing the culmination of not just his improvement in power but also adaptability. The only thing that really detracts from this is Yuren not having any prior on screen feats against other superhumans to build him up as a threat.
I think another less appreciated aspect of the MC's growth, though it extends to the whole party, is the ability to coordinate to take out stronger foes. The way everyone hit the ground running upon encountering monsters of Earth and seamlessly teamed up to kill Gigante with no hesitation is honestly pretty amazing. The MC's growth as a tactician (even if he wasn't alone in it) has improved considerably compared to how relatively awkward his fight alongside Michael at the portal was.