Notes:

Then we see perhaps one of the worst moments of DB as Roshi proceeds to imitate UI and dodges Jiren's blows and forces him to block one of his own.

You can't defend this. Roshi didn't just dodge 1 blow. He dodged multiple ones in a row. Even if you say "Jiren was holding back", this guy's capable to move so fast, he travels from planet to planet by himself without the use of his spaceship, because its faster that way. How much "holding back" can you tolerate from the jump of aged King Piccolo (who might be able to destroy an entire city before regaining youth) to Jiren who surpassed Galaxy Busters. Jiren took blasts from SSB Goku without flinching in the same chapter nor could Goku dodge a blow. Is Roshi faster than SSB? Did Jiren hold back knowing Roshi is insanely slow? He has to have perfect self-control.

Even worse, Roshi retired back in DB. It was to make space for the new gen and acceptance that his time as being a challenge for his studends are up. All of them were trained under Kami, surpassed King Piccolo, some trained under King Kai and surpassed even Nappa. Goku especially learned and overcame obsticals Roshi can't even dream to challenge.
No amount of Character Moments and Peeptalk will change that. This is why I consider Roshi's existence as a competitor in this arc one of the worst ideas in both anime and manga considering the universe is at stake and there are far stronger fighters in Yamcha, Goten, Trunks, Yajirobi, Chaotzu, Mr Popo, any Namekian warrior and perhaps even Mecha Tao Pai Pai.

Which makes it relatively obvious that Roshi is nothing more than fanservice in this arc while adding Goten and Trunks could have opened the gates to actually make them characters.

I honestly believe that Toyotaro did this intentionally. Toyotaro was very consistent with the manga most at the time and from reading his AF manga I can tell he puts a lot of thoughts and efford into his work. I can only assume that he did this to troll people or he is upset over something. Maybe this is his way to payback for being called a tracer.
But maybe the fanfic writer in him did get the better of him and he just did that. It doesn't change that this ch is a complete disappointment.

This is my overall opinion on Ch 39 of DBS.
If Ch 38 was the best of the manga version of DBS, Ch 39 is certainly the worst.