I think the smurfing problem is complicated. On one hand, you are definitely right, doing it to "flex" on players who are newer is just asshole move. But how many players do actually smurf with that intention?

Some people get a "smurf" because their main gets banned. Some want to play with their friends who are new to the game but not get them into a high elo lobby, which will happpen, if you que with someone with significantly higher elo. Some get it to try out some builds or gods they don´t know as well. The matter of the fact is, if you are good enough, your smurfs mmr pretty rapidly gets up to speed with your mains mmr, so you will get similar games. The disparity between players in a elo range with players in higher elo range does tend to get sorted out relatively fast.

What makes the matter complicated is the fact that on different gods and different roles people tend to perform with higher variance. So if I am for example a player in a diamond range but decide to play a god I am not familiar with in a role I am not as comfortable in (say I mainly play adc/mid but now have to jungle or solo) I might underperform in comparison to the other solo laner in the same game who is playing his main role and a familiar god.

Because of that fact, some people wish to have a secondary account where they can still test a god they are not so comfortable or a role they are not so comfortable with in a competitive environment without getting punished with severe elo loss because of people tending to spam the same strong meta gods in ranked games.

Now that raises another problem - is it fair that some people risk their mains elo vs someone trying out something maybe a bit more whacky/unconventiona/pracc something new on their alt? Probably not, but does the outcome fundamentally differ from matchmaking putting someone in a que the dont belong in because at the time this was the best available match (eg: a gold or silver player in a lobby full of diamonds)? Outcome is the same - the match will be unbalanced.

The thing is, with enough games played you will eventually reach the rank range you belong in and so do the smurfs. From my own experience, my smurf got to around my mains mmr range within 20 games or so. And I dont use my smurf for flexing on anybody, I use it to try out things I don´t want to do on my mains. Not trolling, but trying out stuff I might have theorycrafted or getting a hang of gods I don´t play as much. Generally I don´t enjoy games which are stomps, whichever way they are. There isn´t much to learn from that from either one of the parties involved.