Yes, it sometimes is. You should become familiar with the quickest way to adjust the screen brightness of your particular phone. In sunlight, you can turn up the brightness and try to keep the phone in shadow, and while measuring angles, know where the Done button is, so you can press it without watching it.

Keep the phone in the shade when possible, to increase visibility, and also to keep the phone from overheating and shutting down on a warm sunny day.

Trolling Angles supports both Light and Dark color themes.  The Dark theme might work better in some conditions, especially at night.