The reason we have to think of the premiership years is because that's the question
You can't, not incorporate what went before because of the feats achieved prior were all the more standout.
Pep's Man City are great on the eye to watch however I'd put their 100 point last season down to the fact that they had no serious competition - Man Utd where struggling through the Mourinho last phase, Wenger's Arsenal where on their last lap downward spiral, Conte's Chelsea where facing the player tantrums and we where waiting for Klopp's layaway's!
Would last season's Man City be able to face a 42 game domestic league season, along with FA, League and European Competitions, travelling in much slower, lesser quality transport to much more inhospitable places? I don't think so!
Then you have Wenger's Invincibles and The Fergie years and Mourinho's infrequent 2 to 3 year stints at Chelsea...none in my mind would have ever been able to cope with the demands of what Liverpool achieved.
Liverpool achieved a Domestic League and European Cup Double twice in 1977 and 1984 at a time technology and travel was horrible. It took far longer to get anywhere or get information...there was no internet, no sky TV to be able to see in glorious 4k what the next opponent was doing. All information about the next opponent was via our scouts.
If Liverpool did the same double this year it would be great but it wouldn't be anywhere near as an achievement against 1977 and 1984.
You're making several leaps of logic here. As for the technology and advances, that is a tide that has raised all ships. The standard of play has increased because of it, and all teams, not just Liverpool and City are better prepared for it, so it makes things no easier for this Liverpool to gain an advantage over any other team than Liverpool in the 70s or 80s.
Clubs lower down the table (and the leagues) have far more resources now than they did previously. The standard of opposition in much greater.
In the 70s and 80s the standard of play was lower, the distance covered in a match was less, the players were less fit, and the standard of professionalism was much lower. Players would show up to games hung over, be out partying all the time the night before matches and getting drunk, and smoking cigarettes. Even great players like Cruyff who were among the best in the world at the time were smoking cigarettes. You could just as easily say that guys like Souness or Cruyff would struggle in this era.
As for a 42 game season, that is a fair point, but the Champions league itself is much longer than the original european cup, and the group stage alone makes up those 4 games easily. Footballers play more football now than in any other era, with the CL and Europa league having more games, as well as International Fixtures being much more numerous.
If you prefer football form the 70s or 80s because that was your era, that's fine, but it's completely subjective.
To me, United's Treble, and Wenger's Invincibles are unique achievements in the English game, and they have not been matched by any English team to date. Clough and Paisley retaining the European cup with Forest and LFC are also unique among English teams, and no English team has matched or surpassed that feat, so that has to be noted. Similar is Peps' 100 point total, which is a unique achievement. Even Liverpool's most impressive league haul in 78-79 (68 points) scaled up to give 3 points for a win instead of 2 would only be 98 points with an extra 4 games played to Pep's City. Even though they played 4 games fewer, they still won 2 more games (32) than Paisley's Liverpool (30).
Whether this Liverpool (were they to win a double) would measure up against the previous doubles is subjective. But going a season unbeaten; winning a league, FA Cup, and European Cup treble; or winning a record 32 league games with 100 points: these are truly noteworthy achievements that have never been replicated by an English team.