I think the issue is that only one of the guys you played in that flex league was a true 4.0, and even then, his record at 4.0 shows him to be at the bottom of that score band.
From experience playing with guys who are in the flex leagues, they generally play in a flex rating about .5 above where they would play in the full-time leagues. For example, the guys you played in that flex league are mostly 3.5s, with one being a 3.0 and one being a 4.0. They would get rolled in a 4.0 full-time league.
I can see you as a low 4.0. Consistency still matters a lot at that level, and many of the guys that hang on at the middle of that level and below get the ball over but don't move well and don't have any real weapons. You fit that bill; your forehand is loopy, but you get it over and your backhand appears to be fine as well. Haven't seen you serve or return, so that's still a significant outstanding variable.
I think you're rightly taking heat from guys on here, though, on your claims to being a 4.5 or beating 5.0 players. Frankly, the claim about beating 5.0s is complete hogwash; they may have called them 5.0s in whatever league you played in, but you're not beating true 5.0s in Tennislink. Nor is there any evidence in Tennislink suggesting you're a 4.5 for anything other than mixed dubs, which is an entirely different animal than a men's 4.5 league.
I like your strokes. For a guy north of 55, you get the ball over by giving yourself plenty of margin and you're still playing a game well after many of your peers have probably quit. Cheers to you for that.