What you slot as encounters is class specific. Might have changed but as a Champion, it was 2 DPS abilities then 1 that was kinda what you wanted, like the aoe mark or the charge or whatever. Mostly it was all DPS, your 2 at wills were DPS and the one good daily was DPS. DPS class=all DPS abilities. Now you had control wizard and as the name indicates, you had plenty of control, so your skills were control related. You still pretty much always slotted sudden storm and magic missiles as your at will(2nd at will was irrelevant). That did leave 3+1 slots for utility based stuff like the choke hold, aoe freeze, aoe stun and so on but that wasn't as much by choice and more because there wasn't pure dmg encounters anyway so you made with the ones that did the best CC(and they all did dmg too). Part of it was due to awful NWO balance so that quite oftesn you didn't have a choice, you had one ability that was very good and a bunch that sucked, so if the utility ones sucked well tough luck. Also bosses being immune to disables didn't help too much with slotting utility shit.
GW2 has 5 abilities that are tied to your weapon. You can weaponswap to get 5 different ones. One of them is always an autoattack(which has different properties like speed/range/secondary effect etc) then the rest tends to be general mmo abilities, some weapons were damage oriented, other support oriented. The other 5 abilities are static(can swap out of combat like NWO stuff).
As for secondary daily/at will, everything is used instead of another ability. If you use your encounter, you can't use your main at will. It's not like they don't count. Granted all the classes I played had one majorly superior at will and daily so the other slots were completely fucking worthless.
My first point though was simply that saying "GW2 had poor action combat because your keys go to 0" is pretty dumb, even if you assume the 0 part isn't the actual keybindings but the number of abilities(10). 1 2 3 4 5 Q E R T F G C V X Z, not counting mouse buttons, there's plenty of room to bind shit.
The second was that the even more limited slots in NWO didn't really increase diversity of build but on the contrary reduced it and made some abilities unused simply by virtue of not being as good as some others and since you only get 3 slots, you can't afford to slot stuff that's worse even if it's situationally useful. Mind you, GW2 was very much the same to an extent, especially since the 5 abilities tied to your weapon couldn't be changed, so choosing weapons was fairly limited and weapons often went in pairs(like this weapon works with this other one but another weap doesn't cause it uses different damage types than your spec allows etc).
Overall I'd rather do away with the limited ability system until they can figure out how to balance abilities well enough. Also offering modular bar setups is pointless if you don't offer modular passive/talents/aa/whatever setups. If I spec for a particular combat type, that will inherently limit my choices in terms of hotbar abilities to stuff that synergizes with my passives. Giving me the option to slot shit that is vastly inferior isn't really a choice, it's just fluff.