Core should've raised the blocksize at least 2MB while developing LN
They did, the limit is now 4x higher at 4MB.
Biggest ever Bitcoin block was 2.3 MB. That's bigger than the 2MB you're asking for.
because the tech is still unproven
Lightning testing has been conducted on the Bitcoin testnet for over 1 year, and increasingly large amounts of people are using it with the live Bitcoin blockchain (6000+ channels moving around 18 BTC right now).
Lightning payment channels are proven technology, by definition. It's been tested extensively now.
and so many different concepts make it even more doubtful
Name them.
I just don't get it, they could prevent bcash split and still developing LN. Oh whatever will be, will be...
No-one can prevent forks in the code or any blockchain forks caused by forked code. The Bitcoin developers can only do their best to make sure that Bitcoin users stay on the Bitcoin chain, they cannot control the actions of people deliberately splitting the blockchain.