What are you, challenger?
This IS SOLO QUEUE we're talking about.
Like seriously, if first pick is a mid main they're going to pick mid. They're not going to secure a top lane champion because the enemy banned 2 tops. They're going to be happy their favorite mid lane champion wasn't banned and will lock it in before you can even say "hi".
Likewise, the last pick won't necessarily be the least banned role. It might happen frequently because most players don't ban supports and more often than other roles last pick gets stuck with support, but that's never a guarantee. If first pick is a support main and second pick is a mid main and third pick is a jungle main and fourth pick is an adc main, last pick is going to be going top. Regardless of whether all 5 of the enemy bans were directed at top laners (and perhaps 2 of your own bans). Add on to the fact that last pick is likely not a top main in this scenario (odds are 24/625 that each role is mained by each player perfectly, assuming all roles are equally popular [lower if not, which is the actual case]) and therefore your last pick is now forced to pick a champion in an off-role which is guaranteed to have 1 or 2 bans in that role and likely has 3-6.
Have you ever played solo queue? When's the last time you've seen players (that aren't a duo) offer to secure picks for each other? Or coordinate champion synergies with their teammates beyond filling each role and possibly having a small synergy like a top Hecarim gets an ADC who mains Jinx and has Sivir as their back up opt to play Sivir? I occasionally see the support and ADC coordinate a pair that works well together (when the support is actually a support main) but otherwise I've never seen someone say "hey champions W X Y Z form a great comp together" and the team proceeds to pick even 3 of those 4. In the LCS? Sure. In premade 5s? Sure. In Solo Queue? Either you're the luckiest player in the world or you're living in a fantasy.