I doubt most of the millions worshipping Shiva in Linga understand either what the Linga stands for?
Also, your view seems to represent mostly the North of India? South India is abundant with temples filled with Ganesha with his Shakti - who is visualized as a goddess or consort.
My point again is - what is mainstream Hinduism? What you say seems like a skwed and narrow regional view which certainly is not really applicable to the highly Tantric Kerala, the Ganesha-centric Tamil Nadu or the Parashurama belt of Karnataka which is filled with Ganapatya images. Are these not “mainstream” Hindus because their ritual and understanding is much more evolved and sophisiticated than their comparatively myth-driven Northern counterparts? The Southern regions seem to preserve ritualistic purity way more than North India (except in places like Kamakhya which adhere to strict codes).
For example, temple worship is mainly derived from Agamas - Veda and earlier Puranas have nothing to do with temples. If temples are part of mainstream Hinduism, then sexual practices are abundant in most Agamas. So what is this mainstream “Hinduism”? I don’t seem to find one common version across the Indian subcontinent. The very simplistic methods of UP and Bihar are Hindu, the highly Tantric worship of Kerala and Assam are also Hindu, the Shiavagama based Tamil Nadu culture is Hindu, the highly smarta and shrauta influenced practices of Karnataka and Andhra are also Hindu - so which of these is really mainstream? None really, each region has their mainstream aspect, although some are more refined and advanced than others.
I think the attempt to homogenize a largely diverse cultural tradition is extremely counter-productive. There really is no right or wrong way, or in the case of highly diverse Indian subcontinent, a mainstream way. I don’t live in India myself, but it is fascinating to see that most North Indians seem to have little to no familiarity with the South Indian culture, religious and metaphysical, while the Southerners seem to understand the North a lot better. Not sure what the dynamic there is…