Since Bush Whacker is the BASE clicker (and currently the only good one), the other clickers should be worthwhile too, if not outright situationally better.
While it might seem bad for variety to make all of the Clickers scale with passive DPS, it's still one of the best and simplest ways to go (Especially considering the effort required to do a click-based formation). Not to mention, that would work better with the talents and their existing gear too.

However, I can see an alternative path for Warwick: Make sure that his kit and gear is mainly related to CONSTANTLY upgrading passive DPS via clicking. This would require some rearranging of his skills though ofc. This would an interesting alternative (imo), because that could keep "shot"-skills (like Veronica's Fire! or Arachnobuddy's Web Blast) relevant for much longer too. A potential problem, unless his mechanics are dealt with cleverly, is that clicking talents are then potentially wasted for him.

Either way would be fine by me.

But hey, why not give some suggestions. Try to look at them as a whole:

* His ability "Syphon" could be changed into this: "Increases your Click Damage by 1% of your DPS". Much weaker than Swordplay, but it works at full effect regardless of how you position him.

* Basic Crusaders (like Princess and Emo etc) who buff Bushwhacker's Swordplay could be less specific: Their Swordplay-boosting abilities could simply be Total clickdamage-boosting abilities, so they work with ANY Clicker crusader.

* Warwick's Hat gear (which increases his click damage) could instead affect his new Syphon-effect. However, it should then scale like supportive gear does (10/25/50/100 etc) instead of as DPS gear (25/50/100/400 etc).

* Curse of Weakness could affect further clickdamage too, not just passive DPS. This compensates for Syphon's weaker base effect (when compared to Swordplay). That way, his cape's legendary effect also becomes almost as strong as Bush Whacker's hat legendary.

* Now Soul Harvest's splash effects needs a reason to exist (as it could be detrimental to CoW and Syphon's strengths otherwise). Maybe change Curse of Agony into something like this: "Each enemy clicked increases global DPS by 10%. Stacks multiplicatively and unlimitedly, but an enemy only ever counts for one stack each. Each individual stack bonus lasts for 5 seconds, but is refreshed when reclicked. The entire effect resets when changing areas."

NOW he is a Splash-click-Crusader quite worthy of existing, no? :)

To compare them:
Swordplay is 5% of base DPS. 15% with Legendary Wand.

Syphon is 1% of base DPS. 3% with Legendary Hat. Add to it Curse of Weakness's tripling damage and its effect goes up to 9%. Now add Curse of Agony into it: Click just 6 different enemies and Curse of Agony has increased your total DPS by ~77% (1,1^6). Now your click damage is 9 * 1,77 = 15,9% of DPS, surpassing Swordplay. However, his click damage simply gets higher and higher the more enemies gather on the screen!

Thus Warwick is now MUCH better for clicking multiple enemies, but Bush Whacker is better for single target clicking (Then we have RoboRabbit, who ought to be EVEN better for single target clicking, but in a more bursty way, in contrast to Bush Whacker's sustained style).
His DPS support via clicking is also WAY better (+200% damage via CoW and +10% multiplicatively per enemy via CoA), making him a really nice DPS-supporter when his total clickdamage's power might be a bit meh (when you don't have many click-trinkets, for example). I find such a powerful support to be very reasonable, considering it's a CLICKING-based support.

Very well thought out idea. The math all works out by the end to reach BW's effectiveness without just being a flat absorption, so the skills work in an interactive way that keeps things interesting. The abilities themselves are useful and fit the theme of an AoE clicker, so it is not discordant. I can't see anything I would change. Everything works well and seems well within plausibility to be able to implement in the game's engine. Good work, Azamagon.

I actually don't think it would need to be stronger just because the damage splits. That's the purpose of the skill - to take the damage you'd normally be dealing to one enemy and split it over multiple enemies. The damage output is the same. It's just being spread to more than one target. Yeah, each individual target takes less damage than the one target when using BW, but that's the point. The risk/reward factor is balanced that way. Risk = dealing less damage per enemy. Reward = dealing damage to more enemies than usual. That's the power/accuracy/range/speed/cost trade-off of pretty much any ability in any game ever.