I've posted this on the Discord server, but thought it would be good to add it here just in case, as it's the official channel for such things.
Some suggestions for Stormsinger:
I've been thinking about the archetype, and thought that since the theme is not just sonic+electric+cold, but also STORM related, that it would be fitting to have some spells from both arcane and druid lists that are more closely related to the storm theme than some pure electric spells. So looking at those lists, I see three spells that I think could be added to the Stormsinger's spell list (one way to do it could be making them available in cores 2, 4 and 6, for example):
Gust of Wind: Fits the winds from a storm forming theme and can add some CC component for lower levels plus QoL cloud clearer for higher levels, allowing the Stormsinger to have both the power to call storms and to "end" them. Level 2.
Sleetstorm - Again fits the storm theme and is a pretty interesting option since bards have FoM on their spellbooks or on their songs if taking the spellsinger lines. Even if for Stormsingers it comes at a higher level spell than 3, it might be quite useful. Level 3 or 4.
Ice Storm - again, self-explanatory in the storm, evocation CC theme, could be level 5.
The fact those spells all have some CC component also would make up some for losing mass hold in case one chooses to go with Stormsinger's T5, and it makes Stormsinger a full on evocation CCer instead of evocation/enchantment, making it more streamlined if a bit less versatile.
None of these spells are game breaking or op, they just add some more flavor to the Archetype, in my view, also adding better support for the cold side of it.
Fitting the storm theme there's also Call Lightning, Stormrage and Storm of Vengeance, but those are close enough to the Lightning Strike effect to be thematically covered already, I think.
Now, in line with Lynnabel's take that Stormsinger needs to lose something, what I wholehearted agree with, together with adding those spells, be it in the spell book automatically or thru cores or even as SLAs, I'd advocate for a loss of all the enchantment spells that are CC related (charms, holds, dancing, suggestion, etc) and really go all in on the evocation CC theme instead of Enchantment. It would be a good trade off (as long as they get those and maybe other cold spells compared to regular bards) and fits the theme very well in a sense that in order to get the ability to better control inanimate natural elements they kinda lose most of their ability to control animate/live beings' minds. There's still the issue of having Hold Mass in Tier 5 Spellsinger. That could stay as an exception for the investment on another tree, as it's T5 and prevents Stormsinger T5 anyways, and would require to keep the investment on enchantment DCs just for that spell - if someone decides to do all that for just one spell, I feel it's ok to keep it if they want to.
Cheers,
NH