So a light with integrated LEDs can have a lifetime that's much longer than one with replaceable bulbs.
Additionally, the total complexity is a lot lower for lights with integrated LEDs. It's just not true that lights without replaceable bulbs are less environmentally friendly -- in many cases it's the opposite.
preferrably soldered on a big metal part
An obvious solution to which would be soldering the LED to a metal connector that mates with a heatsink. We could call it an "LED bulb".
Of the assorted LED bulbs, fittings and sealed LED only products I've so far owned few have got to even 20% of claimed life before colour temperature or brightness has become pitiful. The only exceptions thus far are in my monitors (not exactly room level illumination), and in a few year old torch - but that has usage in hundreds rather than tens of thousands of hours.
So it looks like we really need some replaceable LEDs. Manufacturers would, of course, prefer to sell another desk lamp or kitchen fitting when the LED inevitably deteriorates.
The market and lamp designers have done this already with LED desk lamps and many formerly standard fittings.
This is not progress, and is both environmentally and financially abusive.