But you and everyone in here has always said radiance is generally a crap item and should only be bought if you can get it quickly, like before 20 minutes.
Yes, but only in a vacuum and not in specific builds. For example, for Illusionists (TB, Naga, PL, Spectre). Radiance is far more effective than many other items because of the damage projection it enables.
If things are rough at all in your lane (which often happens to a Spectra), should you still get it?
There are no hard and fast rules here. You will have to make the judgment call whether to keep pushing for the Radiance or "settle" for a Diffusal. A good question to ask yourself is:
"Are we still in the game? Can we hold out until I go 'online' with my Radiance?"
If the answer to that is "yes", then you should keep pushing for Radiance. If the answer to that is "no", then you should go Diffusal.
Just because you had a hard time in the lane
doesn't necessarily mean your team is being crushed and they need you to bail them out. There's an equilibrium effect in DOTA2 where if one of your lanes is being pressured, then another lane is
not getting pressured and should therefore be pulling ahead to balance things out. For example, if the enemy Pudge is going around getting ganks, then the SF that's afk farming mid should be able to complete a core item (Sblade, Blink, BKB) soon and set themselves up to turn the tides. If there's a trilane suppressing your carry, then they're lowering their own EXP rate and leaving
their solo/mid open to ganks. Identifying when the equilibrium is being maintained, if lopsided, and when your team needs you because they are actually losing on all fronts is the key to answering the question: "Hold out for Radiance or build Diffusal?"