This is a “theoretical” computation of total damages for Clarissa and Gravemaker as defenders and attackers, considering the average 5* defense ( which is 724.3 ) and also a heavy tank (991 DEF, just as a telluria +20 shield path). The damage formula follows from some @yelnats_24 posts and it is assumed that clarissa has +70% direct damage against holy and +33% in DOT against holy (whereas GM has +25% in both against nature), this follows from calculations from other users.
Following results are for damages as attacker:
And the summary of damages as attacker is:
Following results are for damages as defender:
And the summary of damages as defender is:
The main takeaway is that basically either as a defender or attacker in similar conditions Clarissa does around 83-84% of Gravemakers damage, however if both have no emblems or have for some reason crit troops then, it is closer to 85-86%. So the conclusion is that the net nerf for Clarissa is around 15-16% of damage with respect to Gravemaker.
Clearly GM is way ahead as an attack and damage dealer weapon, however Clarissa’s elemental link may be very useful as a “support” in mono stacks or 4-1 stacks. Thus Clarissa is more of a support damage dealer than GM which is not necessarily bad because Purple element has lots of good damage dealers (there are even two S1 five stars purple snipers!) Also the innate resistance of poison of Clarissa may be useful against some defenses featuring Jabber or some other purple (like Proteus as example), but it is rather situational and overall only useful as an attacker.
With respect to defense, because of Clarissa’s class and her elemental link she has way more resistance and survability as a tank, so she is a way better tank (even though dealing less damage) but substantially worse in every other position. She should hold diamond defense without problems.
It seems to me she is certainly worthy of tabards, however roster composition may take part while making those decisions (i.e. you may need a sniper or dmg dealer more, so some other purple 5* may be a better choice).