Switch numbers are okay. Neither the comparison to Switch's last April nor the direct comparison to the PS4 and XB1 this April should be used to declare the numbers great, because the bar is low in either case.
A bit perplexing that seemingly both Sony and Microsoft are targeting a late 2020 launch for their next consoles. Software releases in 2019 have hardly moved the needle on hardware sales anymore and a variety of promotions in the past will lessen the impact of an official price drop in the future. 2020 won't be looking good for them when 2019 already turns into a crawl.
Numbers are always low during this period, However I believe the Switch this month is the second highest April this gen only bested by PS4 2018. So while the numbers are low in a vacuum, number is high for April. So definately more than ok.
But yes I do agree with the rest of your post, if PS5/Nextbox really is releasing holiday 2020.. next year is going to look grim in terms of sales.