"Drivers don't usually try to overtake you if you are indicating right, "
It happens to me on about a weekly basis due to the road layout where I live.
Anecdotes are not evidence.
"yet a lot of cyclists think it's ok to undertake you if you are indicating left and no, it's not "lawful filtering"."
Why is it not "lawful filtering"?
It's for exactly this reason that I take pains never to be alongside a car when passing a junction opening.
You're in slow or stationary traffic. Folk complain about cyclists being in the middle of the lane so we can't go there; moving to the centre line is patently dangerous because as soon as traffic sets off again cars will be undertaking cyclists; so cyclists pass on the left and you don't like that either. What do you expect them to do, levitate?
Left-hookers are all too common and can be fatal. It could be that a cyclist is daft enough to pass on the left whilst someone is indicating to turn sure, but most times this sort of collision occurs when either the driver doesn't indicate, or overtakes the cyclist and then immediately drops anchor and turns. I've seen it happen countless times.
Even if for the sake of argument you're right and it's all the cyclist's fault, will being right make you feel better after you've just killed someone?
You've got mirrors and a neck, use them before turning. It takes a moment to shoulder-check before turning and could save someone's life one day. Contrary to popular belief cyclists don't "appear out of nowhere," you're just not looking for them.