Were cricketers in the 70s and 80s mental midgets or something? “Oh no I can’t bowl well anymore, Viv Richards got out for a brisk 45 two hours ago”.
Unfortunately bowlers back then, unlike today's bowlers, didn't have T20s to toughen 'em up. So most likely those fast bowlers weren't used to seeing batsmen hitting them back over their heads, in any form of the game, and making a successful career.
On a more serious note what probably further made it scary for bowlers back then is, it never seemed like Viv was playing beyond himself while scoring runs at a brisk pace. Holding mentions he found it a bit unnerving to bowl to Viv because "Viv would often smash your best deliveries, and then - knowing fully well what he had done - he would saunter down the pitch with a smirk". I guess bowlers back then didn't fancy any batsman playing like Viv did & being successful for more than 10% of the time, while Viv was successful probably around 40-50% of the time.
In a County match, when Somerset took on Lancs, when Viv came into bat, Lancs unleashed their fastest & scariest bowler - Patrick Patterson - on him. Patterson bowled as if he wanted to kill Viv. A barrage of bouncers were countered with powerful hooks/pulls. 2 overs of Patterson flew for 33 runs, and he was taken off the attack.
Once the statement was made, Viv didn't stick around for long after. Rest of the Somerset batsmen though made merry as Patterson (angry & upset with himself at having lost this particular battle) didn't come back into the attack until much later.
Now, Viv wasn't superman. Bowlers got him plenty of times too. The same Patterson bounced Viv out when Jamaica took on the Islands in a Red Stripe cup match.
Nevertheless, whatever the reason, there's no denying that Viv's batting did have a huge psychological impact on the opposition bowlers, team as well as the audience. It is impossible to truly appreciate the impact, unless you have experienced it live (& especially if you were rooting for the opposition). Scorecards & even YouTube videos simply don't do justice.
On paper/stats though, Viv is definitely inferior to a lot of the names mentioned here (Kohli, Tendulkar etc.), no question about that.