I think in general people do. The concern is that the devs will be splitting their focus and their team between two games, and it potentially splits the playerbase and the economy.
There are some concerns that this means PoE1's issues won't be addressed as well. PoE2 was made to solve many of the problems that PoE1 has, and they continued to develop the game beyond that scope to the point it became it's own product and changed too much of PoE, and because PoE2 is such a significantly different game, it risks alienating their existing playerbase, so they are now preserving PoE1's gameplay, while making the changes they wanted to make for PoE2 which should attract more players.
But that now means that those solutions that were developed to fix PoE1's problems are now only in PoE2 and tied to an overall total rework of the game built around those solutions and how they change the game. Things like how the skill gem system works to be more simple, mana reservation no longer existing, etc.
Ultimately it's no different than having WoW and WoW classic. Just hopefully they'll have a large enough playerbase between both games to justify maintaining both. Their idea of staggering releases does mean that many players will likely swap between the two though and play both.
They did answer in a Q&A later on at Exilecon that the games run the same engine and things can be ported between the games, if there is content that's popular in PoE2 they may release it in PoE1 and vice-versa. The only real thing that cannot be ported is the character animations.
This does also mean that since purchases are shared, MTX have to be made multiple times for the 7 PoE1 character models and for the 12 PoE2 character models.
tl;dr If you like the existing PoE1 gameplay, PoE1 will continue to exist largely as it is now. If you like PoE2 more, then you will have that. And if you like both you can continue to play both and there will be more overall content to play between the two with the staggered releases.