“If I were to reapply next intake year would my application be harmed by this unsuccessful one? Would I have to retake the online tests?”
I believe you do have to give it a cool off period (as you mentioned, it’s usually a year) but it shouldn’t affect your application. I have personally been there myself, I made it to the partner interview of a firm I really wanted to work for (top 20) and I too made the rookie mistake of assuming partner interview was a formality. Once the interview started I quickly realised that I was pathetically unprepared and just felt awful after the interview. I felt even worse when I actually received the rejection letter (didn’t leave the house for a week).
I applied again 10 months later as soon as the intake opened up (I did have to do all the tests and AC again). Once again made it to the partner interview (even had the same partner as before) and this time I was able to put my heart and soul in the interview (it was still a really difficult/stressful interview, perhaps the hardest one I’ve ever done). In the end I was actually accepted.
If you truly want to work for Deloitte then don’t give up! Honestly I think I considered not reapplying again so many times but ultimately I’m so glad I did, as I’m really happy now. If I can give one piece of advice it would be to be honest that you’ve applied before. I personally didn’t bring it up in my second competency interview and I got what can be best described as a ‘light telling-off’ phone call before my partner interview that I should’ve offered full disclosure from the beginning. They found out when they tried to book my personality test and found that I had been entered in before. The partner also mentioned this after my partner interview was over.
Best of luck, hope it all works out for you.