It's not cheating at all. However you want to play the game is fine. If you find yourself not enjoying open play for a bit, dive into solo, why not? At the end of the day, you've paid for a game to entertain you, for enjoyment. However you get that enjoyment is fine. The thing is, people will whine about how unfair it is for other players to not put themselves in the line of fire, but at the end of the day, what does it matter? If a player in solo was forced into getting blown up repeatedly, chances are they'd just not play at all, so them playing solo instead is no big deal.
That said, I generally play in open because I prefer seeing other people flying about doing their thing, and knowing they might try to attack me at any moment. The only time I drop to solo is if I really need to dock (mission timer going and need to go out IRL for example) and the station is packed. Then I'll drop to solo so I can get a bay. They *really* need to put in a docking queue to eliminate that need.