The European business model is VERY different to that over the pond so is the use of regional jets.
Travel within Europe is not really Hub and Spoke centric but has greater emphasis on POINT-TO-POINT for business travel including the LCC carriers and Inclusive Tour Holiday charter flights.
The Regional Jets are therefore employed on developing the secondary and new POINT-To -POINT routes such as BAcx and BMI
from Manchester to say Vienna/various Italian cities and Scandinavia, and Lufthansa/Eurowing from Dusseldorf/Hamburg/Dortmund, PGA
in Portugal, Air Nostrum (Iberia),
Regional Group (Air France) etc.
The ERA (European Regional Airline) Association represents these carriers.
One airline that seems to be slightly different is KLM City Hopper whom actually do fly for the parent out of Amsterdam on what might seem mainline routes and in an almost American Hub-and-Spoke operation which it is as there domestic traffic is just not viable (Well not until the merger with Air France at any rate) AND
FLY INTO LHR
WITH FK50 plus ATR (of Air Excel)
As for Heathrow well the traffic levels on most routes are MORE than sufficient for at least B737/A319.
There has been a long standing reduction in UK domestic routes by BA
to expand the long haul ( Now just Glasgow/Edinburgh/Aberdeen/Newcastle/Manchester all of which again the B737/Airbus/B757 are really used).
fly similar completing routes plus Belfast/Inverness/Tees-Side (For Newcastle)/Leeds-Bradford again using Airbus types.
As for RJ
presence well I think its just (Inc the very few Props these days !)
KLc FK50 to Rotterdam ATR to Eindhoven (Air excel)
FLYBee (Air France) to Lyon with Bae146
Lufthansa City to Stuttgart with RJ200/RJ700 and Bae146 plus BMI
at weekends with EMB145 from Manchester/Brussels and back to Manchester.
Luxair sometimes send an EMB as well but scheduled for B737 normally. About it I think.