No problem with Cilic's or Anderson's quality of tennis. My problem is with guys who are 5'10" or 5'11" trying to compete with them. The best of the latter may be able to break into the top 20 but it's unlikely you'll find them in the top 5. Currently the only sub 5' player in the top 10 is Goffin. He's #10 at 5'11". As good as he is, I doubt he'll go higher. He's 29 and has been on the tour for about 11 years. That's a pretty good sign he's around his peak.
Of course, tennis won't be ruined of all players were 6'4" or higher; it would just become even more serve-dominated. What we have now is a bit like watching an NBA game with a few 5-footers mixed in with the big guys just trying to survive.
I remember watching 6' 1" Sampras bomb first serves and the big serving Safin 6' 4", 6′ 5″ Richard Kraijcek, 6'2" Roddick' huge serves .. Rios, Haas, Hewitt, Agassi still made it to the top.
I don't agree that big tall guys are making ATP bad. College yes, I agree. I had thought under 6 foot is an anomaly and rare. Really tall & under 6 foot just adds variety.
Diego and Isner was fun to watch. We all cheer for Schwartzman anyway. There'll never be a lot of very tall guys dominate ATP or those under 6 feet.
USA's D1 colleges with majority of team players over 6' 6" is dumb because the American power tennis game has proven to be flawed and does not translate to success on the ATP except maybe doubles. where points are shorter.
I recall the avg height for American men was over 6 feet a decade or so ago. Now it is under. I think the US' avg height of men is shrinking likely due to immigration but I am cool with int'l people so no gripes there. (
https://time.com/4423589/americans-shorter-new-height-study/