Ultimate exposure is gained through posting on all successful sites available, and currently tapas and webtoons are two of the most successful ones.
Ditching one entirely because of a slump is a bad business decision, and doing so on repeated occasions will send your audience the message that you're an unreliable creator.
Choose your main site based upon the site's values and main drive. Tapas is my main uploading site because they value free expression, LGBT content, they have high acceptance for expression through mature content, I like their audiences and I see great stability and strengths in their revenue earning systems (in a sense that I can see how it earns the actual company revenue, and thus I can see it still standing a few years from now).
When judging any site you should set up a few preferences/requirements/expectations. You should try to think long term rather than short term. Think long and hard before you choose or change your preferred main uploading site, because to be successful as an individual creator you'll want to be as consistent as possible and make thought out decisions.
Emotions are irrelevant to business, too.
Quick and easy subs may feel good, but at the end of the day you need to ask yourself which site's financial plan seems more stable and which site better suits your morals and preferred audience.
The choice is up to you. Once you've made the choice of which tool to keep as your main go-to, don't blame the tool itself. Because the choice was always yours.