It depends on how "heavy" we're talking; if OP is a student just looking to analyze six or so RNAseq samples for an undergrad thesis project, a laptop is fine. If OP works in a lab where a billion reads is coming off the sequencing machine every week (with an occasional novaseq being performed), then no.
Edit: By "heavy", I had assumed the OP was referring to the latter but if it's just a one-time analysis of 20 samples, I think a laptop is fine. Not sure why one would buy an expensive laptop just to analyze 20 samples though...
Define most demanding because for what I usually do (metagenomics) none of the above would be sufficient.
Full RNA SEQ analysis from raw reads for both short and long read sequencing