Wrightson's 10 issue run ended in June 1974. And While writer Len Wein stayed on the series, it must have been an editorial struggle to replace Wrightson after the series had been nominated and won multiple awards each of its 3 years published.
Nestor Redondo was his successor for most of the remaining issues of
SWAMP THING's 24-issue run.
But there were other possible choices.
Jim Aparo had done some very nice work on the character in the BRAVE AND THE BOLD issues that guest-featured Swamp Thing (the first being B & B 122, Oct 1975, out 16 months after Wrightson's departure).
Both Wrightson and Redondo did shorter stories in DC's mystery titles, so it was logical to pick Redondo, whose stories were right alongside Wrightson's in HOUSE OF MYSTERY and other DC mystery titles.
Looking through back issues, there are a number of "swamp monster" stories by other artists that closely resemble Swamp Thing in many of these DC mystery issues. That's how Swamp Thing began in the first place by Wein and Wrightson, in HOUSE OF SECRETS 92 in 1971!
One I saw that was a very real possibility as a replacement that never materialized was
Arthur Suydam. I saw in an interview that he was offered the assignment but declined it. Possibly because he didn't want to be overshadowed by being Wrightson's replacement, and preferred to go in his own direction.
But I'd recommend two issues from that 1974-1975 era that show what Suydam could have done with the SWAMP THING series.
"Carnival of Dwarves" in HOUSE OF SECRETS 119, May 1974, scripted by Michael Fleischer with full art by Suydam on this 10-page story shows Suydam was artisctically developed and ready for the job at precisely the time Wrightson left the series.
A follow-up story a year later, "Island of Crawling Flesh" in HOUSE OF SECRETS 131, May 1975, emphasizes the point that Suydam would have been an excellent replacement.

Suydam wanted to write his own stories and wasn't getting his way with that at DC and left in 1978, and a few years later was doing his own "Mudwogs" stories for HEAVY METAL and EPIC ILLUSTRATED.