isolated incidents and make it look like it is the norm ... where you get your information from and it is a very poor source
Umm, that´s of course in general a valid point.

Therefore regarding your thesis
I can assure you that England, France, and The Netherlands still have similar cultures to what they had 20 years ago.
I have a suggestion:

Though it seems you did not visit it during your holiday, may I include Germany as France´s & Netherland´s neighbour in your list? If yes, I suggest you study German crime statistics and compare "before 2015" with the development "after 2015" (the year Angela Merkel opened the borders), categorized by crimes and nationalities. Each "Bundesland" (State) publishes the yearly numbers. To make it less work I suggest you just have a look at the crime statistics of "Nordrhein-Westfalen", the state with the highest population (18 million people out of 83).

It´s a highly enlightening not anectodal theme from a trustworthy source (though Germany degenerated we are still not so low that we´d fake our official crime statistics).

If you follow up upon this suggestion I would be very curious whether you uphold or change your opinion.