Yes, because the song kinda sucks.
If you said an arc Against all Odds, Jolders Hammer or Defiant Gravity, then those are usually just as good as tl (though tl still shreds like no other in arc burns).
But the song? Nah
I think, you can't really compare this two weapons, because Song of Ir Yut is a legendary and Thunderlord an exotic, but Thunderlord is a really good weapon. If you have enough strange coins to buy it, do it.
No, Thunderlord looks good on paper but there is rarely a chance to use it, plus it's an exotic so that limits your other loadouts. When Arcburn is on, you most likely want to shoot rockets anyway.
Song shoots through Knight's shields and kills cool down your grenades. Super Good Advice (solar) can kill all 7 oracles in VoG with one magazine whereas Thunderlord can not (it fires so slow in the beginning it's really no use in VoG).
Keep 1 for special occasions if you have the vault space, but also put it on the list of "I need a shard, what can I dismantle?"
I didn't dismantle my 3 songs because they're raid weapons. But they just sit in the same slot all the time. Thunderlord, Jolder's Hammer and Against All Odds are my favourite MGs. Slow fire rates yes but they do more than tickle the enemy (I'm looking at you Song).
I use my thunderlord for any arc burn, two of the guys I play with have it and when we fight the strike boss we switch to field scout, reload, then switch back to perfect balance, three people using it at once will wreck anything, plus it just sounds awesome
Ok best way to put it, go do ursok the hated at skywatch, song of ur yut barely even tickled him with hive disruptor perk, thunderlord 1 magazine takes down his shield and downs his health to a third