Yeah, certianly because of that. If we assume Jura improved a bit from the GMG (or even if we assume he stayed the same), he was a couple of tiers above Erza back in the GMG. It makes sense to assume she improved during the past year to be on his level or slightly above, but not very much above.
So, how do you explain that an Erza who is on par or slightly superior (but very slightly, if at all) than Jura could beat a spriggan with the external help of one character support, while 4 magues on the level or above of Erza couldn't defeat God Serena?
Because God Serena is way superior to Ajeel.
And even if you considered Erza to be leagues above Jura, which would make no sense whatsoever (like, what has she done this past year to become massively stronger than the second or third strongest human on Ishgar?), and, by the way, you'd also be putting her above GMG/Tartaros Laxus, which is very hard to believe IMO; you'd have an Erza that equals to 2x Jura, maybe. Even then, there are 4 magues of the caliber of Jura or superior fighting a Spriggan and they were fodderized. So, however you look at it, the only possible explanation is that GS>>>Ajeel.
Btw, Erza didn't give high difficulty to Ajeel. Once he got tired he used his massive sandstorm and he fodderized. Mid-difficulty at most.