Well, Alexa ranking said to be the basis of how much a site traffic gets.
I think you can compare from there and see if your competitor Alexa rank is higher than you.
That's the best thing you can do instead, since it is not possible to check your competitors traffic.
Competition truly set goal with a view to get better in search scores,the most vital thing is to point out their rating factors and source of traffic.No doubt similar-web is first-rate source to analyze visitors,but still then there are resources to remember like alexa ,compete,SEMRush.
there are many tool to check competitor traffic:
Alexa, SE Ranking, InfiniGraph, Topsi, Monitor Backlinks, SpyFu, Open Site Exploser, Moat, iSpionage, Followerwonk, Simply Measured, ....