Hunters were able to solo a boss in BWL back in classic.
Item squish is not going to affect soloing in any way. GC said that your items are only squished in new content, world and pvp, but in old content your items get boosted. Lets imagine that after the squish your average ilvl is 200, it will stay 200 in new content, but when you enter an old raid, for example naxxramas, your ilvl jumps back to the pre squish 540 (or whatever). Blizzard also might have different ilvl for different old content, just to keep somekind of challenge there.
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I started in TBC I can't quite remember what I were soloing though :P remember using the term and liking the challenge, was very noob back then so probably was something really easy that I thought was tough
Doing SM GY for blue's and gold to save for 100g in vanilla.