Now about number of skills and flexibility. GW2 gives you more skills than GW1 (at least 10) but in terms of flexibility it's more complicated. You have 5 base skills (6-10) and then weapon skills which can be treated as only 2 (slots 1-3 and 4-5). In most cases we have 2 weapon sets which makes it 4 + 5 base. 9 altogether. That's not that much more than 8 in GW1, right? There are ways to increase this number but it usually requires using specific skills so it's really a part of certain strategy.
Are combos underpowered? I don't know, maybe. I recommend you to read "GW2 mechanics" thread, we discussed this matter there, and I'm eager to continue. I remember one of the devs said once "Numbers can be tweaked". If combos will prove to be underpowered in competitive play I'm sure devs will do something about it.