I don't think there is any chance to call Lazio a weak team. They finished fifth in the points table last season as well. So I think Lazio is a strong enough team. This season too, they have performed well in the first two matches.
The important thing is that this is Lazio's home match. Lazio is unbeaten in their last 3 home matches against Bayern. Won two home matches and drew one. So I think this match will either be a draw or Lazio will get full points. A draw seems more likely to me
Last season, their defense was quite weak but that doesn't mean their form was so bad. Conceding 58 goals in one season is a testament to the weak defense they have especially for Serie A matches. This season has not seen much evidence of improvement in the defensive area, but they started the season in a good way
"not losing". That's the reason why Lazio should get attention in today's match against Inter.
While Inter are the team with high goal productivity in Serie A last season and beat 19 rival teams. Inter scored 87 goals in 38 match last season, and that trend looks likely to increase given that Lukaku is still reliable. I think Martinez and Lukaku will score again in this match, and it's 1-3 for Inter to win in my opinion.