He increased the power he utilizes in combat.
You need to realize Roshi back then doesn't utilize his full power form in combat. Every fight we see, even when Roshi extreme diffed Goku in the 21st, he didn't use it until absolutely necessary
Shit he didn't even use it against Piccolo
21st Goku was also a threat to 21st Roshi yet his full power max power kamehameha would've killed his 10x strengthened Great Ape form. There is a huge gap
So...
21st Goku ~ 21st Base Roshi
22nd Base Roshi ~ 22nd Tien ~ 22nd Goku
No, because Roshi says that he would've lost if kept fighting as he was.
Roshi didn't use his full power against Tien, stated by Tien.
Not his full power buff form, his base full power.
That's proven cause his base full power that he actually utilized against King Piccolo has the same exact power level as Goku and Tien.
Not everything is strength. Roshi was amazed that Tien was skilled enough to easily utilize the Kamehameha after seeing it once, and he claimed he could just copy all his other moves.
On top of that, he was a skilled fighter with a deep bag.
When it comes to skill and variety, Tien has it.
When it comes to AP, it's dead even.
Goku in the 22nd and Tien in the 22nd has the same exact power level as Master Roshi against King Piccolo, when he was tryharding, something Tien stated he didn't do against him.
Because this is what you end up implementing
Goku > Roshi's Full Power's Max Power Kamehameha >>> Roshi's Full Power Kamehameha > Base Roshi's Kamehameha > Base Roshi
Effectively making Goku and Tien shit levels above Roshi.
Same Base Roshi who is on Tien and Goku's level.
They would be different, because the Daizenshuu notes a difference between the Kamehameha used on Frypan and the moon busting Kamehameha as completely different techniques, just like Goku's Kamehameha and his Super Kamehameha