Like a lot of code regs, there's some over-engineering built in. Is a good thing for the most part but for various reasons at times you really want to do what will be adequate to work, but less than fully code legal. I'm doing a bathroom remodel now, was made twice as big, the new vanity is 8 feet away from prior plumbing and this is on a slab.
I also needed to spin the toilet 90 degrees, and to get optimal distance from both walls (in a corner) I needed to move the drain back and over a couple of inches. It made the most sense to tie into the toilet line for other reasons, and the need to move the toilet made it a no brainer. I found out however that hooking into the closet arm (the J shaped piece leading away from the toilet before it passes under the vent) is a no-no.
Would have made massive more work to go on the other side of it. I researched it hard, found a plumbing forum where some actual plumbers gave me good feedback.
Most were down on the idea. When I suggested that I up the drain from the sink, and vent servicing that drain (tied over to the main vent up above) to 2 inches from 1.5 one guy said he thought that would work if I turned the inlet on the Y fitting into the closet arm up 45 degrees. I gather that the problem with hooking it that way is that flushing the toilet can create a vacuum that will suck the water out of the sink trap.
I hooked all of my stuff up (the client wanted the toilet hooked back up for my use so I wouldn't be using the tenant's toilet (he has two housemates) so this gave a great chance to observe matters before covering it up with a tile floor. I installed the old toilet and put in a cheapo 1-1/4 plastic trap on the sink drain fitting. Sure enough, when flushing the toilet the water in the trap would move up and down some but was not pulled out. I suspect my improved venting helped.
Here's my thread on that, maybe the forum could be useful to you. Shortly after I joined they switched to a different format, advertising now dominates half the page. I could swear participation dropped off. I don't like it much. Still usable but ...
https://www.plumbingforums.com/threads/hooking-drain-for-new-sink-into-toilet-line.12892/#post-97489