Right. It just not something that most DIYers can do. I have been personally straightening decks for over 10 yrs now and still a PITA to do most times. I think the worst deck I had to straigthen in the last year was my own deck. Basically I park my mower on top a large stump while the deck was engaged.
That why I both MIG and Gas welders, grinders, and other tools to reform these decks. Sometimes it requires cutting and re-welding areas due to over stretched metal. I have gotten fairly good both types of welding but I have been doing it for 20 yrs too.
You got do all this while maintaining the alignment of all the moving parts. Just because you get the blades back to their level plain doesn't mean all the moving parts are working correctly.
I do get in decks that have been welded with stick welders that just looks plain horrible. Stick welders are not meant to be used on sheet metal, too much heat.
Basically it take a lot patience and a few headache pills for me.