I tend to prefer comics that don't overload on text. While some exposition is necessary, I prefer it be done through dialogue - and that that dialogue feel as natural as possible. Assign it to a talkative character, or someone in a position to teach/mentor, OR have the person listening be ignorant of the facts and need them explained - have the character explaining present the info as befits their character; irritated, know-it-all-y, in a confused mess, etc. Whatever works.
I'm not too big on narrative boxes with info-text in them. Those work, but I prefer if they, too are in a character's voice, rather than omniscient voice. Comics are a visual medium, and there are strengths in that. Give me them pictures!
Also, there is a lot of power in not giving all the info. Breadcrumbing your backstory/mythos/worldbuilding/lore over a longer period of time is something that shouldn't be undervalued. Giving the readers the info piece by piece not only allows you to spread it out and prevent pages that are 80% text, it also gives your readers something to do while they wait for the next page; they get to speculate and theorise and therefore become more engaged in your story. Webcomics, by the nature of the format, tend to post slowly - a couple of pages a week at most - so there's a lot of waiting involved on the part of the reader. Giving them something to do while they wait is nice!
Breadcrumbing also lets you build mysteries, leave spaces in the story for that mystery to grow, and on the whole, feels more natural. Because at the end of the day, the characters in your comic inhabit their world. They don't need big expositionary explanations of stuff - they're aware of the rules and lore of their own world already. Unless they encounter something truly unfamiliar, they're not likely to need big speeches - or info-dumps through narration boxes - to go about their lives. Conveying information to your reader by breadcrumbing will feel less stilted, and will certainly result in fewer walls of text.
Of course, it all depends on what story you're trying to tell, but honestly, you can trust your readers. If you've got two characters in a scene obviously antagonising one another, and one of them throws some insult at the other along the lines of "You wizard-scum!", you won't need a big text-box - or multi-page prologue! - explaining that wizards, in your world, are considered second-class citizens, because your readers can put two and two together and come up with four. You can reveal whatever lead up to the circumstances of your world through dialogue and story-events.
.... Hi, I'm Anna, and I have read too many high-fantasy novels, and am therefore allergic to wall-o'-text-y prologues and exposition, no matter what the medium. Your mileage will certainly vary.