Not having 1v1s here doesn’t mean the SH’s aren’t getting stronger. They can fight in a team against people and still get strong enough to contend against the next opponent. Luffy has demonstrated this. Blackbeard is a long ways away, they don’t need to be ready for that right now. They have time. You’re also underestimating them to an extent. For instance, Nami has Zeus and probably will retain him past the arc. She would have a weapon that a Yonko used going into the fight against Blackbeard. By the time she got there, and had progressed through the New World, she’d get stomped even with Zeus?
Its fine for them to grow, like Luffy has grown. They don’t need to be entering peak strength during this fight. That’s not how it’s ever worked in OP. It’s likely that the only time the SH’s will be outright stronger than their opponents from the outset is when Luffy is the King heading into the final war.
1. The majority of team battles have either been one sided stomps (straw hats vs Franky family, and straw hats vs zombies) OR long drawn out, RPG style fights (straw hats vs oars, straw hats vs pacifista). None of these fights were all that amazing in displaying the straw hats individual strengths. Against the Franky Family and zombies it was like cleaning up trash and one shotting or low diffing everyone. While against Oars and the Pacifista it was just chipping them away until they fell down. They used teamwork and sneaky ways to overcome the enemy but that's it. They don't really get a whole lot stronger this way, because those victories required a team effort, it wouldn't apply to future battles very much if they didn't have others around to help them. Like the Brook and Nami Lightning Bon Advant combos against Oars for example. In a fight against the Blackbeard pirates and Straw hats where each crew will consist of 10-11 members on both sides, we can't just have team ups and leave some blackbeard crew members free with no opponents. That just means they can gang up on the other straws which only makes things worse. Luffy vs Blackbeard, Zoro vs Shiryu and Sanji vs the third strongest, Jinbe vs 4th, while the rest have to team up just to defeat a single blackbeard pirate, they'll run out of people before they can beat them.
2. I've never liked Nami getting the zeus powerup. Nami is only strong in a fight when she doesn't get into a challenging close combat. She can only fight against enemies from a distance, and once she loses her baton or her arms are restricted its over for her, just like how Charlotte Galette stopped her easily with her butter.
3. I also disagree that they have time. It is because of the lack of fights, Oda is now forced to just hand out powerups to the straw hats on a whim. Nami get Zeus, Sanji gets Raid Suit, Zoro gets Enma etc. This is despite the fact that Zoro hasn't even gone all out yet, Sanji haven't had a Jabra like fight yet where he pushes himself to develop a new technique like Diable Jambe (Sky Walk was only learned during the timeskip so that doesn't count), and Nami's last 1v1 fight where she improved herself was against Kalifa of CP9 and learned the new mirage and lightning attacks(not counting the timeskip training). After that Nami has been relying on outside help ever since, like Ussop to upgrade her climate baton and stealing zeus to get stronger. The only person that Oda made time for was Luffy, where before his fight against Kaido, Oda had to cram in 3 1v1 fights for Luffy against, Doffy, Cracker and Katakuri, just so Luffy can be able to take on Kaido in Wano. And in all 3 of those fights Luffy needed outside help, he couldn't beat them on his own, granted this doesn't matter much since taking down Kaido is most likely gonna be a team effort anyway with Kidd and Law. But what about against blackbeard? Luffy needs to beat him on his own.
4. It's true that they don't need to be at peak strength now, and its also true that they won't reach peak strength even if the 1v1 opponents this arc. But at the rate they are going now if Oda doesn't have them improve individually now, then it just stays like this and the longer we get closer to the final war, the more powerups and upgrades Oda has to give to the straw hats and hastily cram into the story just for them to be ready. We can't just have the straw hats always getting powerups, but little to no fights.