There IS a difference though:
the old I-L was kind of additional to the train-network, linking towns without rail and routes without direct trains, of which this is the best known and long lasting example. The longest was Lelystad-Emmeloord-Heerenveen-Groningen, now broken in E-o as it would give the newly opened rail too much competition.
These routes also cannot really be compared to the Brit N-E/Mega network.
The now newly set up routes are kind of National Express/Fernbus.
Railfares as such are not low at all anymore in NL, but its more that any frequent trainuser will have some kind of railcard. Students go for free, so the main market for such weekendlinks has been sapped. (I myself, senior now, pay 20 eur/month for unlim. weekenduse and half fare offpeak weekdays). The 1 eur fares are also gone-kind of RYAN imitation introductions. In all it remains to be seen which routes will in the long run attract enough people to remain viable.
The secretary of state resp. for publ.transp. in her new days and in a mood against NS has decided that some competition might give hopefully NS a kind of kick in the ass and thus allowed it.
Yes, there is a difference, and that is what I was really saying in the last point. The Qliners are designed to complement the rail network, rather than compete with them. Clearly Flixbus, by contrast, are hell bent on competing as much as possible.
Here is a comparison between current fares and fares in my 98/99 Spoorboekje (24 May 98 - 29 May 99) on page 833.
2nd class singles (full fare) for selected distances:
0-8 km
1998: NLG 3.00 = EUR 1.36
2015: EUR 2.20
Increase of 62%
50 km
1998: NLG 14.75 = EUR 6.69
2015: EUR 9.10
Increase of 36%
100 km
1998: NLG 26.00 = EUR 11.80
2015: EUR 16.60
Increase of 41%
150 km
1998: NLG 34.75 = EUR 15.77
2015: EUR 21.30
Increase of 35%
200 km
1998: NLG 43.50 = EUR 19.74
2015: EUR 24.60
Increase of 25%
250 km
1998: NLG 54.50 = EUR 24.73
2015: EUR 25.70
Increase of 4%
Long distance singles have clearly gone up the least (a big reduction in real terms) because both the single and day return were capped at the dagkaart price (NLG 71.50 = EUR 32.45), whereas now the maximum fare applies at 242 km.
Inflation since 1998 is about 37%. So I don't think we can say that fares are "no longer low". The only fare that has gone up a lot is the very short distance fare.
Obviously the fares above can be reduced by 20% or 40% if you have the relevant railcard. With fares that low, I can't see much scope for Flixbus to compete on the routes like Amsterdam to Rotterdam unless they are charging 10 euros or less.