LBS just need to be canny and they can compete. My LBS has a club with £5 per year membership, for that you get 12% of parts accessories and clothing. They don’t keep massive stock, but can order anything, and you still get the discount.
If you look at crc wiggle etc, most of the stuff that is normal size, current model, and in stock is only 10% off. I ordered an endura mtr emergency shell for £79, much cheaper than online.
Unfortunately the discount doesn’t apply to bikes, so my next one will be from canyon.