we had this in my company it was pretty hit miss. Almost always the 'TLM' was someone who was in the role for a really long time and it warranted a second person, so it ended up being a 1-2 junior reporting in absorbing the knowledge that the tlm had.
If you were in a growing domain, and the TLM stayed engaged with the code it worked really well, but as soon as one of those failed it was a bad roi for the company and a pretty terrible experience for everyone. the juniors were never getting promoted since there was only room for 1 expert on the small domain. The TLM was just chilling getting 5-10% raises a year without going outside of their little kingdom, but making sure their domain worked well.
As their junior got better they coded less but their juniors couldn't grow as long as they were there because the niche didn't need that many people.
I don't think its a coincidence that all these companies eliminated these rolls after 2022. When you have unlimited money and massive headcount growth these roles can exist and give your good but not exceptional people room for career growth. At static headcount, you basically need to do what banks do -- yearly cuts or no one can be promoted or hired.