[wwn_se]

It really depends on the project as a consultant I have seen crazy complexity on both "sides".

Most projects backend seems to be more complex but backend also get more slack. For example if there is a DB performance problem there is usually a DB-team to help with tuning.

Front end ppl are usually more on their own, since its expected they will have easier problems. That's not always true though. Some orgs are adapting and adding css specialist and design roles to enable more technical front end devs to focus on that.