Dude, aside from the fact this is opinion either way, and as such the 'backing up' line is complete bunkum, neither yourself nor anyone else has ever asked that question of me. So play the condescending, false **** with someone who does give a ****. That's one road you DON'T want to travel down.
That said, as you have now asked, in my opinion, you've glaring holes across the board, both in the starting XI and depth.
One position you are as strong as anyone, if not out on your own, is in goal. So no need to touch that. The defence however is another story. RB's a mess. Ivanovic has dropped off a cliff, with little else to replace him. Even inverting the Spaniard there, you'd be starting what should be depth in Rahman at LB. So you're at the least lacking depth behind him. And he ideally needs upgrading IMO. Centre half is even more of a cluster ****. You're bringing back Terry FFS. His influence might be sorely needed in that dressing room (more on that in a moment), but there comes a time when you just have to accept you can't cut it at this level. For the club, even if he won't, that time should be now. But he's currently in line to start with Zouma being out. Cahill has followed Ivanovic off that same cliff, so unless I'm missing someone, there's only Zouma coming back off his injury outside of those two VERY iffy vets. I actually like Pedro, so your wider options are sound with the excellent Willian and Hazard. Although the latter's attitude over the course of last year would be starting to ring alarm bells for me. But we disagree there as we have discussed previous so we'll move on. The middle is very weak to me. Matic is quality in his role if he regains his form, but there's no one of any note either backing him up or alongside him. Fabregas may come back to the fore, but he's dipped considerably the last few years and is coming off another very poor Euro's showing. Oscar? Great if you only want him to play the first 3 or 4 months of the year. Mikel is a useful squad player, but then you're down to inexperienced kids. Traore and Kennedy I know little about so I can't say what they may or may not become. Loftus-Cheek looks fairly promising, but has a ways to go to be anything like a regular. And up front you've even less. Costa I've never rated as anything approaching a top striker. Two good career years over a decade and more and never cutting it at all on the International stage does not a top striker make. Remy who should be decent depth doesn't get a look in at all for some reason. You've started to address that in the Belgium who a French friend tells me has the potential to be a very good forward, if currently well over priced. (Although that wouldn't bother me. It's the market today with the extra TV money.). So at least you're acknowledging that. But I wouldn't want to rely on him as the main man coming from Ligue 1. BIG step up to put that on his shoulders. Not least when he's still developing. You certainly need another at the least anyways.
So that's a a VERY light squad on quality, not only in depth, but in some key starting positions for me if you're seriously considering getting back up there. Certainly the worst by far IMHO of the now big 5. 6 if we say Tottenham's now in that traditional discussion. And after the disgraceful attitude of most of the players week in, week out last year just mailing it in and sulking, I'd be seriously concerned to the overall attitude within that camp with no real leaders there pulling everyone together in the Chelsea cause. But that's just me. Maybe Conte harmonises the group.
Don't see you as any sort of a threat to the top 4 spots at all as you currently stand but time will out on that.
This is of course just my opinion that I know from reading you greatly differs to your own. But thank you for finally asking. Do that earlier next time hey mate when you have a problem instead of letting things fester, then resorting to the arrogant **** and inferring things that never were?