I would agree Everton are crap but they have been circling the relegation drain for a while now so it is not new or specific to this season is it? It is normal that the teams around the bottom do not look good that is why they are where they are just like every season. The only big change this season is Chelsea dropping off so badly despite spending a much more than anyone else. Citeh, Arsenal, Man U and Lpool remain good teams, Spurs are normal for Spurs and now NUFC, Brighton, Villa, Brentford and Fulham all have good teams so this argument the the PL is the poorest ever just does not really stand up. It is more competitive now that ever before with more teams who are capable of getting points of each other. I think the ONLY reason people here say the PL is poor this season is because we are 3rd, if it was Brighton in our position you would not be saying this.
If you think Sunderland would be OK without significant investment than is up to you. I can't see that to be honest as you don't really have a strong squad in terms of quality, depth or experience. You best player is on loan (so quite possible needs to be purchased or returned to Man U) you only have 1 real striker as far as I am aware and he seems to be injured more often than he plays. Hence my view significant investment would be needed.