You're quite right. I was talking about Lufthansa 'mainline'.According to https://www.lufthansagroup.com/en/company/fleet/lufthansa-and-regional-partners.html they have CR900s, E190s and E195s, not to mention Air Dolomiti's large Embraers (with whom BM also has a codeshare).
Agree that these are all substantially larger than the BM ER4s, but they are broadly the same size as KL operates to BRS. SN also have Q400s in their fleet, albeit they have retired their 4-engined regional jets. Of course, understanding how these aircraft are currently used may preclude their deployment on routes ex BRS.
Pricing of LH connections tends to be uncompetitive relative to KL and SN. Perhaps with larger aircraft operating to/from BRS they could secure a greater share of the market by pricing realistically for non-business markets.
When LH operated to BRS in 2008-2009 they used Eurowings Bae 146-300s - 100 seaters, or thereabouts - at 3 x daily (21 x weekly) that was probably an overkill. They reduced in the first and only winter but by then the recession was at its height so it might not have been a fair period with which to judge the seat provision.
bmi regional seems to come out every year and say they are looking at securing larger aircraft, even if not for the entire fleet. I remember a couple of years ago a senior officer of the company used BRS-FRA as an example of a route that could do with larger aircraft.
The good news today is that bmi regional doesn't seem to have suffered any cancellations.