Yes, I also always thought, since the beginning really, that Federer followed Agassi, and that Agassi's fabulous style influenced tennis as a whole much more than Sampras' style. It was really great to see Andre play for those "extra" years, kind of reminds me of these Roger's "extra" years. But both Roger and Andre placed the ball and constructed the point, on any surface really, and that is also what made them excellent on clay.
However, that is not first strike tennis as you mentioned, not at all. That point building style is what delivered Roger as piecemeal to Rafa's point deconstruction and obstruction, and made him an easy target for war of attrition, each and every time they met. Roger continuously wanted to build any point, on his serve or not, and Rafa first deconstructed it, and then wore him down. Point by point, game by game, set by set. Seen so many times. Agassi would have adapted better and faster to that, he would've shortened the points in any way possible. Roger just played along instead.
Sampras, Becker, Ivanišević didn't place the ball to build the point, they hit a winner, or at least finished the point with max one extra shot. It's an entirely different game for the defending player when you know it, just watch how helpless most opponents were against Sampras, as they knew he is going for it every but every single time, end of discussion.
A very large racquet head like Agassi's wasn't for easier attacking but for easier blocking, returning, and reactive play. Surfaces and balls were faster then, serves became a huge weapon with taller players and better racquets after 17yo Boris "Bum Bum" Becker won Wimbledon in 1985 and then again in 1986 and Sampras later perfecting that style. Small racquet heads they used, and Federer later, is what is always associated with attacking tennis, they are way more precise for serving and attacking, especially in the old days of heavy flexy racquets and gut strings. Agassi knew already as a youngster that he doesn't have that kind of serve so he decided go turn that tactic upside down and have the best return, good move. And yes, I also thought back then that Wilson should've given Roger a ~95 to more easily handle high jumpy balls and more modern tennis. Also, I'm not sure but I think that old PS85 was really an 88, so the transition to a 90 was super easy. I played with a 2007 K88 made for Sampras for several years, it was 345g but easier to swing than 340g RF97A.
Tennis then evolved towards slower balls and surfaces, lighter stiffer larger frames, more spin, faster movement on court and that is where Roger had to eventually adapt towards a larger frame. For a good single hander you need a racquet that doesn't twist, that's why Stan has lead at 3 and 9, and why new Roger's racquet has high twistweight. So a narrower head helps for example, maybe a larger grip size etc. While a larger head helps with modern faster spinnier play as the sheer surface and sweet spot are larger. But every racquet I tried larger than 98 was too wide, too much twist on the backhand, so I don't think that larger than a 98 is just better for a single hander, no way. A 95 to 98 is ideal for a single hander I'd say.
But to get back to Rafa, the only way to deal with that intentional slowing down is to punch through and consciously not allow any point deconstruction. Many of us do it against weaker or defensive opponents, it really isn't some special philosophy. Best recent example is Čilić - Musetti in Miami last week. Čilić did everything right, and wiped the floor with Musetti, who is still young, but who very clearly couldn't deal with intentionally shortened points by Čilić, who totally rushed him and was fully aware of the success while doing so. Rarely do I say "well done" after watching Marin, but there you have an ideal example. Rafa is a better player than Musetti of course, but it was obvious that Rafa clearly knew what was going on already in IW and Miami 2017 and later in Shanghai 2017 and Wimbledon 2019. It was clear to him that he has to play a match where all points last 3 exchanges, more only if Roger is in the driving seat. He knew he was losing already at 1:1 in the first set.
How Roger hits the backhand is part of that awareness, Ljubičić clearly explained to him that he is working against himself if he is slowing down the game with slice backhands all the time, and obviously convinced him that he has to force topspin backhands practically at all times just to rush the opponent, to speed up the point, since that almost always goes to his favour. That particularly applies to opponents who like to slow down the point, like Evans recently, or Rafa of course. He should only use the slice when he's the one needing time and being rushed, and that is not that often.
New 97 sq in racquet isn't always ideal for one handed backhand, especially flatter ones, it is a bit too stiff for the smaller tendons on the back of the shoulder, and it is heavy to move. So to play topspin backhand with it Roger really has to be conscious that he is the one forcing it and rushing his opponent, and not allowing opponents to slow down the point. He has to invest a lot of energy into it, as it is much easier to block it with a slice backhand. That is why over the years Roger became lazy about it, slicing a lot, again. When you see him continuously hit topspin backhands you can clearly tell that he is not playing around, and that he is taking his tactics very seriously.