Of course it's not needed for a maxed out PUP. But hey, not everyone IS fully comfortable with PUP or has the same gear or familiarity.
Honestly, if you're needing Repair at all, you're either doing something wrong or under 100/1200 JP. And if you're under 100/1200 JP, yeah, this ring probably does make a significant enough difference to improve your kill times meaningfully.
If you're planning to do a lot of Ambuscade on PUP and don't really need the use of a TVR ring for the rest of the week, why not use the easily available excellent option? Drop ring, book warp to Xarcabard right next to the Dyna entrance, pick new ring. Takes less than a minute. Can repeat after every Sunday.