Seeing as how every WZ except huttball always requires someone to be guarding the off node, 1v1s are somewhat important.
PTs also drop like a little ***** when FFed. They also really have no utility outside of pull. Sents have almost as much burst, but much better surv and way more utility. And people were complaining about PTs just as much as sents before 1.4, but PTs got nerfed quite a bit so people don't complain about them as much.
Replace the sent in your situation with any other class, and guess what? It's even worse off for the healer. Also, the fact that everyone KNOWS sents have all these abilities makes them unlikely FF targets. CoP, camo, GBTF are all deterrents that force teams to FF anyone but sents first.
Any other class in that situation would be dead, whereas the sent comes out with 1/4 of the HP still. That's a huge difference.
True, but not every class is suited to node defending and balancing to account for 1v1s with all classes would be a disaster. Node defending requires the classes that are best suited to it (mara, op, sin, sniper arguably, potentially others). PvP as a whole means that this cannot determine balance, you just have to roll with it.
PT burst is significantly stronger than marauders and cannot be countered well outside of a long cc. Can't be interupted (like ravage), cleansed well (like annilihation) or kited well (like rage). They do drop quickly when focused which is exactly as it should be, they are a class cannon, burst balanced by lower survival.
Note that UD is a defensive cooldown,
of course they're going to be better off if they use it, what would be the point otherwise? Other classes have access to other defensives, but the nature of those defensives mean they should be used at a different time. UD just before death, most others just before damage is taken (clever applications aside).
I agree with your point about not focusing marauders first. This is perfectly fine as they can be countered well enough to avoid needing to be focused immediately. A good team will notice when the cooldowns are used and focus then if need be.