I used a spectre for the first time

So I was struggling a lot with the green monster''s second phase and hadn't used a spectre once in my playthrough, so I thought, why not give it a chance.

With the spectre, I first timed it using without healing.

While I'm happy I bested the green monster, I kinda feel disappointed with myself because summoning a spectre feels like cheating after all.

Does summoning a spectre trivialize every boss, or is this only the case for the green monster?