When I first started posting my comic, I was only interested in posting to Tapas because I knew from experience that the community was amazing and very forgiving towards new content creators such as myself.
However, after a year of only posting to Tapas, I decided to post my comic on Webtoons as well. After all, exposure is everything for small creators. My original reasons for not posting to Webtoons, some of which you've already pointed out such as having more sites to keep up with and splitting traffic, included Webtoons' rating system and the vertical scroll format preference.
I didn't like the rating system because I didn't want to receive poor reviews and ultimately become discouraged with my story. I've been told many stories regarding users purposefully giving comics bad reviews to tank their rating. I don't know how true or not those claims are, but the thought of it happening to my comic really put me off posting to Webtoons.
As for the vertical scroll format, I do single pages once a week. This isn't ideal for Webtoons as they tend to prefer longer updates.
In the end, I can honestly say that posting to both Webtoons and Tapas has only improved my audience overall. I don't regret splitting my reader base because just having people enjoy my comic was enough for me!
I hope this helps with your decision!