In my opinion, the pricing is OTT, for the product offered.

Sadly, I get the impression that TG have rather given up on First and are just milking the LHR route while they can.
I am still using them mainly to run down my miles and upgrade vouchers.
I do value the direct flight and i find the seats are pretty comfortable, food offer is variable.
i have another BKK/LHR round trip in First (award ticket) coming up next month after that i will probably switch to EK or LH/SWISS.
Last time I checked there was 100000 plus baht difference (P fare) between THAI and EK for LHR return!

The agent i use says that many of her regular THAI premium customers have also switched to alternatives for European flights.

BTW when i flew out of LHR a few weeks ago I was told the Sing lounge would be closed for refurb until July.