Is the XAT exam tougher than the CAT exam?

Yes, as the questions are a bit more difficult than CAT in both quant and English. 

• VARC can be a bit difficult, if you have not focussed on topics of critical reasoning and decision making in your class.
• Quant sees a number of questions from inequality, progression, boolean algebra, PnC and the general level is higher than CAT. 
• The percentile-score balance and cut-offs for top 5 colleges which accept XAT scores, have low requirements. 
• People aren't able to get those scores also because the exam is tough. 
• XAT is easier because it is largely predictable. 
• CAT is famous for being very unpredictable. 

So XAT is tougher than CAT by the level of questions asked. But as their paper is largely predictable it makes it comparatively easier to attempt.