Why is engineer so good?

I have been trying to play engineer but I just can’t figure out why ppl like it so much. I feel like the damage isn’t all too great (pls correct me with statistics if that’s right bc idk how to upgrade properly) and honestly I like accelerator better besides the lack of stun immunity. I’m trying to fit both into my loadout but I can’t because they are super expensive and take up 14/20 slots if I do them all which doesn’t let me have farms, dj, or my crowd control, so I’m just a bit confused.