Filemaker pro 13 is over 250mb to install in some cases. So yes, the amount of UI/UX data it needs to push to a user for webdirect for "the filemaker experience" requires a lot more horsepower than the simple functionality of IWP. There have been many articles over the past few years about optimizing your solutions for WAN performance. You can have a layout with one field, but load 100,000 records and make that field a summary and boom, bad performance. I'd imagine there will be continuing articles from the community with similar performance tips for webdirect. As it's been out less than a month, there's not a lot on webdirect yet as a lot of developers are still playing with it.
As for your text issue, I'd try removing all the styles first to make it a plain unformatted object, then re-adding the attributes one by one, seeing if it breaks anywhere.
It's a first release, not everything will be perfect!