For reviewers they are usually least bad, but still bad. For example Manuscript Central still requires pop-ups and can be more or less impossible to use with mobile devices. It also has separate login for all journals and password rules that makes it very common for people (including me) to have to reset the password every time they need to log in.

For editors they tend to be a lot worse. E.g. with Editorial Manager adding reviewers is really painful and the search is totally useless. The process to add and be added as a reviewer takes multiple messages in a quite confusing process. Decision letters are sent with bizarre template hacks that are really easy to mess up.

Some submission systems still require formatting of images etc to some arcane formats like tiff and eps. Or to have figures and captions as separate pages. These cause significant work for submitters and are a disaster to review.

Compared to typical enterprise systems they could be even worse, but I'd say still worse than average in that class too.

Don't know if these are a significant barrier. For me they have been and I've resigned as an editor due to the unusability. But I find that they easily cause enough loss in time and nerves of authors, reviewers and editors to be of negative value.

I will admit that MC is pretty annoying. Particularly the issue of having separate login/passwords for all journals. I haven't been in the position of Editor at this point, so I can't speak from that perspective.

I haven't yet run into submissions systems as arcane as those you mention in terms of format requirements, but that does indeed sound very messy and I hope I never see it.