Should I switch to mirrorless?

Right now, I work as a car photographer using my Rebel T5i, but I have been considering upgrading because of a few reasons;

1- The performance on high ISO is very poor, anywhere after 1600 ISO, it starts to get grainy.

2- I somewhat like the auto-focus, but better autofocus, especially in darker spots such as the interior will make life a lot easier and make my pictures better, I tried using my 50mm f/1.8 lens to take close-up pictures of the interior and the auto-focus gets really bad with that lens for some reason.

3- Battery life is enough most days, it lasts around 6 hours on a single battery so I am not concerned about it, but longer battery life would be great.

Overall, I really love the camera, it's been with me since 2020 and I have taken some really amazing pictures with it, but now that it is more of a job than a hobby, I think it is time to upgrade.

I have been thinking of 2 options

1- 5D Mark IV because I saw a picture my friend took at 8000 ISO and it looked better than my 800 ISO,

2- R6 Mark II, which I know is a little more expensive, but everyone talks great about it and mirrorless is the future of photography, which is what I plan on doing for the rest of my life

I just don't know which one I should spend my money on to be my camera for at least the next 5 years, on one hand I have 4 EF lenses and 2 EF-S with a lot of great lenses on the market, or if I should spend extra money on the R6 since it'll be the future and I should learn more about mirrorless before I'm too late

My budget is $2500, and I would be willing to buy a used camera as long as it is in great condition.