It should be pretty difficult to actually max out path units - there are people with cities >500k cims without maxed path units, that is certainly not the issue
It has been known for a while that the large pedestrian area service points and the newer "city quay" actually break the pathing in the game - they can't "release" any used or broken paths so the number of pathing units used will just climb and climb and climb until it hits the max and then you're done playing that map. I'm unsure if any of the other "larger" garbage-only or goods-only service points break the game or not since I get by just fine with the small ones
Anyway, you can completely solve the issue by doing all three of these things:
A) Replace all pedestrian area service points with only the small one (the one you start with). Use multiples if you need more garbage and goods. I have three pedestrian areas - one uses 5 small service points, another uses 4, and another uses 2
B) Replace all segments of the "city quay" in your entire city with a different quay. I haven't had any issues with any of the quays from the workshop, Avanya has some really nice looking ones!
C) After doing A & B, you need to use Transfer Manager CE mod to release the broken path units. In the last tab in the mod settings, there is a button for "Release Broken Path Units" or something like that (can't remember the exact wording)
After that you should be good to go, as long as you never use those assets again
(I can confirm this is still the case as of yesterday, since I decided to try and use the "city quay" around my new university to see if it still has pathing issues. My path units shortly maxed out at 524k within several hours of placing the first quay wall. After replacing them with different walls I used TMCE to clear the pathing units, and it said it cleared over 380,000 pathing units!!! I have been happily playing since, hovering around 130k at all times)
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