No, I don't think Dimaria is being overrated at all. She would one-shot Erza if she had her time magic so restricting it only makes it quite even except the difference in power between Erza and Dimaria herself.
First of all, if there is any character that is not being fairly assessed here, it is Chelia. Is she strong? Not in my book. So why do people think Dimaria is weak after last chapter? Because she was defeated by Chelia, a medium tier mage.
Now the difference here is that Chelia is not just he normal self. She has Third Origin which is being severely underestimated if anything. If we think back, Second Origin allowed Team Natsu to achieve 7 years worth of catching up in training. I think the reason why SO is underwhelming for some is because Erza used it to defeat Minerva. Forget about that. Some PoF was involved, although not entirely. Third Origin obviously surpasses SO, even more than 7 years. Literally, the only reason why Chelia beat Dimaria was because of Third Origin. Did that part appeal to me? No. In fact, it was complete nonsense. It was so overpowered that Hiro Mashima had to put restrictions on it like losing your magic power after using it. Like I said before, people with hax magic are usually going to go down due to a clear weakness or PoF/hax magic involved. In this scenario, Dimaria lost her hax magic while Erza doesn't gain one like Chelia did. Erza is going to lose against a Spriggan.
Honestly, I don't know where you're getting the information from but since when did Wendy and Chelia tank Dimaria's attacks? I don't see Erza and Dimaria being too different in speed. Dimaria can fly and Erza can't. Armors like Erza's or Dimaria's has no major impact on a battle in Fairy Tail because it doesn't add much defense to a person's durability. There is no way we can say Erza has better CQC than Dimaria because Dimaria was able to match Kagura and Erza is really not too much stronger than her. Nakagami wouldn't necessarily kill Dimaria. Remember that Dimaria has strong durability, especially after being punched and unfazed by DF Wendy.
I already gave my explanation about TO. Now it is up to you to agree or disagree. If you want legit feats, I'll provide you some.
One of Wendy's stronger DF attacks did no damage to Dimaria. Same with DF Wendy's punch. At the same time, Wendy is hurt by Age Scratch.
Wendy Immobilized by Dimaria's Beam
Yes, there is a huge power difference between Wendy + Chelia and Erza. DF Wendy closes that gap quite a bit but not too much. Third Origin Chelia pretty much surpasses anything that Erza has besides Nakagami Starlight. Now, let's see Erza's feats. She is pretty strong especially for holding back Ajeel and making their battle a tie without Third Origin. However, she did receive help and still didn't defeat Ajeel like planned.