A bit late, but, eh, here goes nothing. In all the cases, Seraphina wins. Let me explain why.
1. Seraphina is one level stronger than John. Seraphina's level is 8.0, while John's last recorder level was 7.0 and he hadn't used his ability since then. Even if he could copy her ability, which he can't and I'll explain below, he would likely be unable to boost its stats. 2. So you ask, "why can't he copy her ability". There are many reasons for that, but let's start with their levels. At 1.2 John could basically not do anything. He couldn't copy other people's abilities, and even if he could, they'd be ten times weaker. So, chances are he can't copy abilities that have a level greater than his. Now, on to another reason why he can't copy Sera's ability. Remember Juni? John likely couldn't copy her ability for one reason. He couldn't see it. The same likely goes for all other mental abilities, which is why John couldn't stand up to Keon. Now, for Seraphina. Her ability also has to do with time, like Juni's. Maybe that could be the reason by itself, but let's continue. Seraphina's ability doesn't enhance her. It manipulates time. And as we all know, we can't see time, can we? John also can't copy an ability iof he's frozen in time lmao. Yes, John's ability is strong, but it isn't Godly. He can copy abilities, but that doesn't enhance his level to that of those abilities. He has a pretedermined level, as seen in the leaderboard, in which he is placed second to Seraphina, which (surprise) means Seraphina is likely stronger than him. We also need to take in mind that the gap between 7.0 and 8.0 is much larger than the gap between 2.0 and 3.0. John's ability also has limitations. He can't have more than four abilities (maybe only if they have high potential), he can't copy passive abilities, and he can't copy abilities that he can't see.
Even if he somehow had all the abilities he's used before... What can a statue do against the flash?