Probably not over a long period of time, but in any given season yes I believe we can be as good as Benfica. We'll need prolonged Champions League football and to continue doing the good things we are off the pitch in recruitment, backroom staff etc.
I think Salzburg are the best comparison for us in Europe right now, with them coming from a similarly sized league to the SPFL. They've been a conveyor belt of talent for years with Mane, Minamino, Upamecano, Haaland and Naby Keita all having spent time with them, and are evidence that with the right infrastructure you can compete at a high level in Europe even with financial limitations. If we make a success of the buy low and sell high model we're aiming for, it will look something like Salzburg do right now IMO.
If we do want to reach that level though, our fans are going to have to get used to us selling players far more regularly than we have historically. Although I think there is an awareness that players will have to be sold, I'm not sure our fans are quite ready to accept the extent to which this will be necessary. I think the situation between us and Celtic competing at each others throats every season lends itself to the club not necessarily selling its assets at the best time; Celtic right now are evidence of that - Ajer, Christie, Edouard and Ntcham will all have one year left on their deals at the end of this year, thus depreciating their value as assets, and have been kept in pursuit of domestic success and keeping us at bay instead of for the long-term health of the club.
If you contrast our rivals decision making with Benfica, you can see a clear difference. Benfica have sold Ruben Dias and Joao Felix recently for mega bucks, and in recent history you can also throw Ederson, Renato Sanches and Victor Lindelof off the top of my head as players who they've sold for good money. Despite them having more threats to their dominance in Portugal than us or Celtic, with Porto, Braga and Sporting all potential title winners in any given season, Benfica are ruthless in selling their assets for the maximum price available with no regard for how it might affect their success domestically in the short-term, as they have faith that their recruitment is good enough to replace the outgoing players, and the infrastructure at the club (youth development, coaching ability) will allow players to thrive. This is the situation we need to aspire to, even if as I said earlier I believe it is most likely for us to be on a smaller scale, akin to Salzburg.
I guess what I'm saying in a very long-winded way is that yes we can reach Benfica's level in any given year, but likely not on as consistent a basis and more akin to a Salzburg level team. But, to do this we will need to continue developing our infrastructure, and not allow ourselves to fall victim to the complacency and short-term thinking that has been prevalent in the east end over the past few years. We can be a success in Europe, but to do so we have to not allow ourselves to sacrifice our business model in favour of short term success - we will be successful in Europe if we plan to be, but if we start to make decisions that prioritise immediate success over the clubs long-term future, we will have much shorter boom and bust cycles that will make it hard to compete at a good level in Europe regularly, as Celtic are finding out right now.