A question about Parry...

Take it when levelling up, respec it out when you softcap. If you're not going the expensive route with HOs in active defence and enough recharge to keep it double stacked so that you have huge defence debuff resists then you might want to keep it.

Defence above 45% is useless 90%+ of the time, so at reasonable level, you would only need to have a single application at any time, and could concentrate on higher DPS attacks.

You can keep it when at 50 and integrate it into your attack chain, but I believe it will cut into your DPS.

Parry and Slash do almost the same damage (Parry does a tiny bit less damage but recharges faster and costs less endurance). The difference is that Parry provides a 15% defense bonus to you (which functions against all MoBs you are figthing) while Slash provides a 7.5% defense debuff (which can be resisted) against a single target.

If the choice is between one or the other then Parry is the way to go.

If you can afford the inf to soft cap you can afford to increase your global recharge speed. In this case you are better off skipping both of them since it will increase your DPS. (even with as much as a 1 second gap in your attack chain).